[HOT] Few Tasking Manager updates

[Dražen Odobašić]

Hi all,

I've deployed a few fixes to the main server, so if you have any problems, first
try to clear your browser cache, and reload the service.

In short:

* Revise lock / unlock procedure to avoid contribution edit conflicts for a task
https://github.com/hotosm/osm-tasking-manager/issues/186
* Improve "show user tiles on map" performance
https://github.com/hotosm/osm-tasking-manager/issues/189
* Highlighting finished tiles based on timestamp from the stats tab.
https://github.com/hotosm/osm-tasking-manager/issues/199
* Invalidate / Comments info lost if later split the job
https://github.com/hotosm/osm-tasking-manager/issues/200

Dražen