dmap: provide a hierarchical view of media database

https://bugzilla.gnome.org/show_bug.cgi?id=723574

Signed-off-by: W. Michael Petullo <mike@flyn.org>
dmap: Use #define for constants

https://bugzilla.gnome.org/show_bug.cgi?id=723574
dmap: Add missing file in POTFILES.in

https://bugzilla.gnome.org/show_bug.cgi?id=723574
dmap: Replace g_warning/debug by GRL_WARNING/DEBUG

https://bugzilla.gnome.org/show_bug.cgi?id=723574
dmap: Use C comments

Do not use C++ comments.

https://bugzilla.gnome.org/show_bug.cgi?id=723574