lightmediascanner: Update to 0.5.1, improve

We update "lightmediascanner" to its latest version,
which also allows us to :
- remove mentions of former company (now dissolved)
and website (now migrated to GitHub) ;
- properly split all plugins into subpackages ;
- have a new plugin based on libav, "generic", which
we do not automatically enable because of the well-known
licensing restrictions of its parent package.

MP4 plugin is disabled, because it depends on the MP4v2
library, which we do not have.

ID3 plugin requires a patch, already sent to upstream :
https://github.com/profusion/lightmediascanner/pull/19



meta-openembedded's only dependent recipe, "enjoy", has
been verified with this change.

Signed-off-by: Manuel Bachmann <manuel.bachmann@iot.bzh>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>