Document Launch flags and Preference directory for findpath

Change-Id: I150c0ca1e0deb5749689bb1019a48efdcdc99def
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6701
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Reviewed-by: nephele nephele <nep-git@packageloss.eu>

BRoster docs: force be_roster to link, lang cleanup

Fix BRoster::Launch documentation const mismatch

Style fixes to BRoster, move docs to doxygen.

Keep the brief description as a regular comment above each public method.

Leave the docs of private methods.

Some variable renaming mostly because of abbreviations.

Add documentation for all the public methods and app_info members and defines
that didn't have docs in the cpp file.

BRoster docs: force be_roster to link, lang cleanup

Fix BRoster::Launch documentation const mismatch

Style fixes to BRoster, move docs to doxygen.

Keep the brief description as a regular comment above each public method.

Leave the docs of private methods.

Some variable renaming mostly because of abbreviations.

Add documentation for all the public methods and app_info members and defines
that didn't have docs in the cpp file.