packagefs: Support blacklisting entries in packages

In each installation location, it is now possible to create a settings
file "packages" that allows to blacklist entries contained in packages.
The format is:

Package <package name> {
EntryBlacklist {
<entry path>
...
}
}
...

<package name> is the base name (no version) of the respective package
(e.g. "haiku"), <entry path> is an installation location relative path
(e.g. "add-ons/Translators/FooTranslator").

Blacklisted entries will be ignored by packagefs, i.e. they won't appear
in the file system. This addresses the issue that it may be necessary to
remove a problematic file (e.g. driver, add-on, or library), which would
otherwise require editing the containing package file.

The settings file is not not "live". Changes take effect only after
reboot (respectively when remounting the concerned packagefs volume).

find_path*(): Support user specific home directory

No longer hard-code the home directory path. Instead ask
find_directory(), so we get the correct one for the current user.

Remove B_COMMON*_DIRECTORY and kCommon*Directory constants

* This does intentionally break source compatibility, so that a review
of concerned code is forced.
* Binary compatibility should be maintained in most cases. The values
of the constants for the writable directories are now used for the
writable system directories. The values for the non-writable
directories are mapped to "/boot/system/data/empty/...", an empty or
non-existent directory, so that they will simply be skipped in search
paths. Only code that explicitly expects to find something in a
B_COMMON_* directory, will fail.

Initial changes to remove /boot/common

* find_directory() and hard-coded paths use /boot/system instead of
/boot/common.
* The build system creates the writable directories in /boot/system
instead of /boot/common.
* The build system no longer installs any packages in /boot/common.

Remove /boot/{apps,preferences} symlinks

And adjust all remained occurrence in the tree accordingly (->
/boot/common/{apps,preferences}).

Fix the etc path that was accidentally changed.

Rename the package links directory

Rename the package links directory from /package-links to just
/packages.

Move <directories.h> to headers/private/system

Create /packages symlink on boot

Rename the package links directory from /package-links to just /packages
and create it when booting.

Move <directories.h> to headers/private/system

packagefs: Support blacklisting entries in packages

In each installation location, it is now possible to create a settings
file "packages" that allows to blacklist entries contained in packages.
The format is:

Package <package name> {
EntryBlacklist {
<entry path>
...
}
}
...

<package name> is the base name (no version) of the respective package
(e.g. "haiku"), <entry path> is an installation location relative path
(e.g. "add-ons/Translators/FooTranslator").

Blacklisted entries will be ignored by packagefs, i.e. they won't appear
in the file system. This addresses the issue that it may be necessary to
remove a problematic file (e.g. driver, add-on, or library), which would
otherwise require editing the containing package file.

The settings file is not not "live". Changes take effect only after
reboot (respectively when remounting the concerned packagefs volume).

find_path*(): Support user specific home directory

No longer hard-code the home directory path. Instead ask
find_directory(), so we get the correct one for the current user.

Remove B_COMMON*_DIRECTORY and kCommon*Directory constants

* This does intentionally break source compatibility, so that a review
of concerned code is forced.
* Binary compatibility should be maintained in most cases. The values
of the constants for the writable directories are now used for the
writable system directories. The values for the non-writable
directories are mapped to "/boot/system/data/empty/...", an empty or
non-existent directory, so that they will simply be skipped in search
paths. Only code that explicitly expects to find something in a
B_COMMON_* directory, will fail.

Initial changes to remove /boot/common

* find_directory() and hard-coded paths use /boot/system instead of
/boot/common.
* The build system creates the writable directories in /boot/system
instead of /boot/common.
* The build system no longer installs any packages in /boot/common.

Remove /boot/{apps,preferences} symlinks

And adjust all remained occurrence in the tree accordingly (->
/boot/common/{apps,preferences}).

Fix the etc path that was accidentally changed.

Rename the package links directory

Rename the package links directory from /package-links to just
/packages.

Move <directories.h> to headers/private/system

Create /packages symlink on boot

Rename the package links directory from /package-links to just /packages
and create it when booting.

Move <directories.h> to headers/private/system