Added ability to retrieve widget/plugin by its pubsub key
Implemented basics of two-step query mediation (plus feedback; will be useful for spinning wheels)
Updated README, configuration
Implemnted two-step query mediation + reworked tests

Now the site feels more responsive and we have ability to react to
problems
Fixed a bug in metrics widget: it was modifying every query cause it listened to START_SEARCH

Also updated query_mediator to allow synchronous operations

Updated unittests (3 to go)
Updated tests (+ fixed bug in minimal_pubsub)
Changed defaults of query_mediator to be used directly in the website
Merge pull request #206 from romanchyla/two-step-mediation2

Two step mediation2