Modification of the interface of the mananger.

The manager now supports messages such as Stop and start for specific
queries. But since we won't use them, I'll remove them and simplify the
manager. I just commit them in order to have a trace of them if we want
to use them later.
Simplification of the TweetManager

Since we will use only a static division of the map in subsquares
(no dynamic querying, where we subdivise a square into subsquare),
I removed some functionalities not needed by the TweetMananger.

Additionally, I nested this one to enforce singleton.
Merge branch 'master' of https://github.com/TweetAggregator/TweetAggregator

Conflicts:
	app/models/SearchModels.scala
Merge branch 'master' of https://github.com/TweetAggregator/TweetAggregator