fixup! Add a schema file

Try and improve readability of the descriptions for format specifiers
and add missing composer format specifiers. Reword some other
descriptions as well.

Add gettext/gesettings type to POTFILES.in

https://bugzilla.gnome.org/show_bug.cgi?id=625897
Check base_uri is a directory

https://bugzilla.gnome.org/show_bug.cgi?id=625897
Add fallback file and path patterns

If the file pattern is empty then all the ripped tracks are written to
".ogg". If the path pattern is empty then all ripped music ends up in
the same directory. The default patterns were removed in commit
49b5a5785 as they were not synchronized between sj-main.c and
sj-prefs.c. Adding two utility functions solves this problem.

https://bugzilla.gnome.org/show_bug.cgi?id=625897
fixup! Port SoundJuicer to gsettings

https://bugzilla.gnome.org/show_bug.cgi?id=625897
Make schema name and dbus name match.

The gsettings documentation recommends that the two names should
match. As changing an existing dbus name in probably a bad idea change
the schema name instead.

https://bugzilla.gnome.org/show_bug.cgi?id=625897