HaikuDepot: reflect package install changes

This update will mean that HaikuDepot is able to detect
install / uninstall actions on packages at the system
level and reflect this in the user interface.

Fixes #15879, #15994 and #15046.
Relates to #11674.

Also cleans up disused code in the WorkStatusView.

Change-Id: Ide2d5d93c2f71915bc7cfe7d3628e5f343e43f35
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4145
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

HaikuDepot: add work status view

* Add new WorkStatusView which keeps the user informed about what's
happening. It's a status bar at the bottom of the window which
shows on the left side either a spinning barber pole (for
operations without a progress), or a progress bar (for download
progress). Next to that is a text view showing a descriptive
status text.

* Currently, it will notify of the following operations:
- Repository refresh (barber pole)
- Background packet actions, like preparation of install or uninstall
(barber pole)
- Package downloads, including downloads of dependencies (progress
bar). Status text indicates the name of the package currently
being downloaded (if any), and how many more packages are queued
for download after it (if any).

* Hooks into PackageListView to be notified of package status changes
(such as becoming pending or download progress)

* When the package currently being downloaded is also selected in the
list view, the user sees the progress bar in WorkStatusView
as well as the one in the PackageInfoView, which is redundant. This
still needs a good solution...