Added checks for backwards compat on MediaTypes
Merge pull request #945 from metamx/MediaTypeFixes

Added checks for backwards compat on MediaTypes
General Caching Query Runners cleanup

* Add type strictness to CachingClusteredClient.
* Add background caching to CachingClusteredClient. Gives between 0% and 5% query speed increase.
* Add @BackgroundCaching annotation for injected ExecutorService items
* Add `numBackgroundThreads' configuration options to CacheConfig (default 0 aka same thread legacy behavior)
* Add unit tests for CacheConfig
* Add an abstract caching query runner class, currently it doesn't do anything exceppt simply make the two caching queries distinct.
* Add caching to CachingQueryRunner. Gives up to a WHOPPING 40% reduction in query time on HLL queries
* Updated docs with more info on cache settings.
Merge pull request #936 from metamx/cachingRunnerImprovements

General Caching Query Runners cleanup (40% query time reduction for HLL)
Changed all "application/json" to MediaType.APPLICATION_JSON  except for in druid.js
Merge pull request #946 from metamx/MoreMediaTypes

Changed all "application/json" to MediaType.APPLICATION_JSON  except for in druid.js
fix jackson-annotations version dependencies
Move some config description from Configuration.md to the Broker and Historical config pages
Merge pull request #947 from metamx/configUpdates

Move some config description from Configuration.md to the Broker and Historical config pages