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>

Moved per user post install actions to first-login script.

* The same mechanism (and the same PostInstallScript) is used for this.
* If a file first_login exists in ~/config/settings/boot, the first-login
scripts are launched, and the file removed.
* This fixes adding the deskbar tray icons even when there is no Deskbar
running yet (for example on first boot when the FirstBootPrompt
starts), or, IOW bug #12275.

Added post-install script, and start UserBootscript again.

* This is the final missing piece of the former boot process.
* Removed the unused Bootscript, and Bootscript.cd files.

Added post-install script, and start UserBootscript again.

* This is the final missing piece of the former boot process.
* Removed the unused Bootscript, and Bootscript.cd files.