HaikuDepot: Added "prominence" member to PackageInfo
HaikuDepot: Retrieve prominence values from web app
HaikuDepot: Separate MessagePackageListener...

...into MessagePackageListener and OnePackageMessagePackageListener.
The first one doesn't know which package(s) it's listening to. But it
can filter the change notifications now and only react to certain changes.
The second one knows which package it's listening to.
HaikuDepot: Add some getters to Model.

For category, depot and search terms filter.
HaikuDepot: Only list featured packages once.
HaikuDepot: Properly add featured packages.

 * Rework existing package listener mechanism to report any interesting
   changes. Listen for prominence changes in addition to package state.
 * Add featured packages to the FeaturedPackagesView when their prominence
   is retrived, and also in _AdoptModel().
 * In _AdoptModel(), show the featured packages view when no search filters
   are active and installed packages are not shown either. Otherwise show
   the list of all packages matching the current filtering.
HaikuDepot: Feature packages with prominence <= 200
HaikuDepot: Move selection message constant to MainWindow.h
HaikuDepot: Select clicked featured packages
HaikuDepot: Fix click detection in featured packages

Take window activation and parent bounds (a featured package scrolled outside
the visible region within the parent) into account.
HaikuDepot: Improve featured package items

Show the summary instead of the version. The layout still sucks, but I will
have to implement some kind of row/flow BLayout to get what I initially had
in mind. Another TODO is to highlight the clicked item somehow.
HaikuDepot: Show a "Featured packages" label

Also remove the left-over separator in the Tools menu.