HaikuDepot: Minor GUI string changes

"Shutting down" is too reminiscent of a system shutdown.
We're just quitting the app. Going with a generic "Cleaning up".
Correcting the app name, HaikuDepot.

Change-Id: Ifadf533170dc89befc971ea86b7140d3aa7fcef8
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5605
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

HaikuDepot: Shutdown Handling

Improvements to the shutdown handling mechanics so that
if there is an install etc... happening when the
application is quit that it will wait until the process
is complete before actually terminating.

Change-Id: I8d3c4fbd9de0abc9382d55f0a6955b7f63a36637
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4322
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>