Bundle Tracker 3 inside the Flatpak
This is a follow on from !146 (merged)
With this change, the Totem flatpak bundle will contain Tracker Miners 3 and will start tracker-miner-fs inside the sandbox in the case that it's not available on the host.
Marked WIP as it depends on unmerged changes to grilo-plugins, however, the CI artifact can be used for testing already.