This results in a slightly larger apk (e.g. 500KiB), but it reduces the
scope for bugs greatly. We still get all the benefits of only having to
maintain a single density-independent vector (rather than several
density dependent PNGs and all the work that involves).
The class of bugs that it solves is that there are several places where
vectors cannot be used, and you wont notice when developing on a device
newer than 5.0. For example, notification icons, `TextView`
and its `android:drawableStart` attribute.
Fixes#913.
* Show selectable background behind "Show/Hide apps" button.
* Scroll to the relevant place in the list when showing/hiding apps.
* Only show one line (ellipsized) of the apps to update in header.
Alows for more flexibility in what we are able to display, including:
* Prompting users to donate to frequently updated apps
* Showing messages from package maintainers to users
* Marking apps for later installation when offline
Most of these are not yet implemented, but will be able to when
required, whereas they were not able to in the previous UI.
