FCmdrGSettingsBackend: Remove unused definition.
Add FCmdrProfileSource.

Abstract base class to fetch profiles from a remote source.

Adds a new dependency on libsoup for SoupURI, but we'll need libsoup
anyway for fetching profiles over HTTP.
Rough in an HTTP profile source.
Add fcmdr_profile_new_from_stream().
Teach the HTTP profile source to fetch profiles.

Current method is fetch a JSON index of filenames from a specified URI.
Each indexed file should contain a JSON profile.
FcmdrService: Hack in a profile source for testing.

Talks to the server.py script in fc-profile-builder.