package: add tweaks for supporting multiple entry-points

pkg.name is changed to the base name of the entry point,
org.foo.bar.App, and it is used for the resources, icons and such.
The name given in the params is used for the installation directories
and gettext domain.
Rename package distribution to org.gnome.Weather

Drop the final Application, which is reserved for the actual
application. This is in preparation for having a
org.gnome.Weather.BackgroundService, in the same package.

This in practice just moves the installed files around (sorry
packagers!). The biggest change is the gettext domain, from
org.gnome.Weather.Application to org.gnome.Weather (because the
background service will also need translations), but it looks
like damned lies will cope just fine (uses the module name).

GSettings schemas, desktop files, appdata files, icons etc have
not been renamed, because they belong to the application proper
(and because renaming them would be a compatibility break).

Finally, the git repository and official tarball is still
gnome-weather. But don't tell anyone ;)
CurrentLocationController: fix desktop ID
Split between the application and the background service

The main reason for the split is to avoid doing geolocation
in the service that handles the search provider (which causes
the geoclue indicator to appear for every shell search).
In the future, the background service will also handle severe
weather advisories, if enabled (and will be able to do so
across sessions, if launched on the user bus).

And besides, it is clean this way too.