We used to implement our own caching and timeout mechanism on top
of GIO's, and our own "blacklisting" that would merge or transform
events depending on the previouly cached content.

This adds quite some extra latency in some cases on top of
GFileMonitor's rate (up to 2s), and even in some cases do produce
mistaken results (CREATE(a)+MOVE(a->b) != CREATE(b) if you are rewriting
a file, but how can TrackerMonitor know).

The code has been simplified in various fronts:
- (Almost) no event caching. Only CREATED/UPDATED events are possibly
  cached awaiting for the CHANGES_DONE_HINT that must follow them.
- No event manipulation nor merging. GFileMonitor does a good job at
  being truthful, and the upper layers do know better how to coalesce
  events into a more reduced set of equivalent tasks, since there's
  further info like file state in the database.
- The deprecated SEND_MOVED flag has been replaced by WATCH_MOVES. The
  MOVED_IN/MOVED_OUT/RENAMED events can be handled in a simpler way each
  than the deprecated MOVED event.

Overall this makes TrackerMonitor slightly more verbose (but still
consistent wrt sending a meaninful sequential set of changes), but more
reactive overall, since we now solely rely on GFileMonitor rate limits.

With this change, TrackerMinerFS is left as the only place that does
coalescing of events.