libmediaart: new package

Library tasked with managing, extracting and handling media art caches

https://github.com/GNOME/libmediaart



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[Thomas: add entry to DEVELOPERS file, fix license file.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>