Fold miner-apps into tracker-miner-fs

Turns desktop file extraction into a tracker-extract module, and makes tracker-miner-fs 1) index relevant dirs and 2) handle locale changes. This basically takes over all functionality from tracker-miner-apps, and thus drops it.

The primary focus here is memory footprint. This miner is not that big in memory, but there's systems where every meg counts. There's also the side effect that .desktop files across the inspected bits of the filesystem are now indexed, this is probably just relevant for ~/Desktop though.