Moved BJob, and JobQueue into the support kit.

* Put it in the BSupportKit namespace, following the style introduced
with the package kit for now.
* The BSupportKit::BJob class no longer knows about the package kit's
Context class. However, the BPackageKit::BJob class does.
* Due to the namespace juggling, a lot of files had to be touched.
* The JobQueue class remains private.
* Due to the way Haiku is built on itself, you cannot build this change
under Haiku with an older release.

HaikuDepot: Organized source into sub-folders

Moved BJob, and JobQueue into the support kit.

* Put it in the BSupportKit namespace, following the style introduced
with the package kit for now.
* The BSupportKit::BJob class no longer knows about the package kit's
Context class. However, the BPackageKit::BJob class does.
* Due to the namespace juggling, a lot of files had to be touched.
* The JobQueue class remains private.
* Due to the way Haiku is built on itself, you cannot build this change
under Haiku with an older release.

HaikuDepot: Organized source into sub-folders