Merge branch 'shantanu-sinny-media-caching'

This implements a media cache for PMC which is populated by one or more
media sources. The media sources can be plugins, currently the one that
we have pulls data from Nepomuk.

The media cache is stored in a SQLite database and accessed using an ORM
layer called ODB. The README, especially the build instructions have been
updated. If you have trouble building or have a concern, please drop an
email to plasma-devel@kde.org

Finally, PMC now also contains test for the new media library code and hope
is that the core libs/ will get good test coverage soon.

CCMAIL: plasma-devel@kde.org