freebox: Add new Freebox TV source

This source will show a list of TV channels available through
the Freebox server, offered by the Free ISP in France.

https://bugzilla.gnome.org/show_bug.cgi?id=720436
build: Required glib 2.32 or higher
dmap: Get rid of g_clear_pointer() function

Not available at glib 2.32.
freebox: Get rid of g_clear_pointer() function

Not available at glib 2.32.