Remove the concept of a short application ID

The way this was implemented relied on the application ID having only one '.'
char. This breaks heavily for new-style GNOME3 applications, and isn't actually
required anyway.

This solves org.gnome.Contacts being deduplicated with org.gnome.Nautilus.
Require the description when searching installed applications

This slows down the initial search as we might need to parse AppStream metadata
(if not already loaded) so we can show the multiline description in the search
results page. In most cases there will be no speed regression.

This will only make a visible change when an application has local AppData, but
no long description in the remote AppStream metadata.