Package Kit: Proper Installation for First Boot Packages

Do the final installation operations for all the packages in the
/system/packages directory when the OS is booted for the first time.

This will run their post-install scripts, create users, groups and generate
settings files (marked with a package version attribute). Previously we just
ran all the shell scripts found in the /system/boot/post-install directory
(don't do that as much now).

Fixes bug #14382

This patch has simpler code flow in CommitTransactionHandler::_ApplyChanges
Tested on 32 and 64 bit systems. Once it's official, need to remove the
open_ssh redundant post-install script that creates users etc. from HaikuPorts.
Now we can notice bugs like package version attributes on settings files aren't
fully working. :-)

Didn't remove special case for add_catalog_entry_attributes.sh since it
still does stuff that the build system doesn't do. Might be able to add
that script as part of the Haiku.hpkg. See change 3751 for removing it,
https://review.haiku-os.org/c/haiku/+/3751

Change-Id: I3807b78042fdb70e5a79eca2e2a45816ece0236f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2342
Reviewed-by: Alexander G. M. Smith <agmsmith@ncf.ca>
Reviewed-by: Niels Sascha Reedijk <niels.reedijk@gmail.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

package kit: Add pre-uninstall scripts feature.

Just like post-install scripts which run shortly after a package is
installed, pre-uninstall scripts are run just before a package is
removed. Implements enhancement #13427

* Fix script exit code handling vs script launch errors.
* Bump package and repo file version numbers due to new attribute,
unfortunately makes new .hpkg files not backwards compatible.
* Add pre-uninstall functionality, mostly cloning the post-install
except in a few places.
* Discover that _RunQueuedScripts() is never called, a future TODO:?
* Update package documentation for pre-uninstall scripts, and use of
the boot/post-install directory.

Change-Id: I45596255ce74bc102f6e5b606cbf83e4e4347a17
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1504
Reviewed-by: Alexander G. M. Smith <agmsmith@ncf.ca>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

Clarify .PackageInfo user creation arguments.

Change-Id: I4f0ea6da53d4793a5128324af2b99d460b67b523
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2576
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

docs/develop/packages: convert wiki to rst

Cleaner syntax compared to MediaWiki, more features than Markdown, while
still looks good on plain text.