overhaul of config reference, first pass
Major edits including the following:

* Emitter module is logging
* readTimeout for http client module 15min
* Fixed broken link to ZooKeeper.html
* Clarified druid.processing.numThreads is #cores - 1 or 1 if #cores == 1
* aws storage section moved under deep storage
* Added more info on various monitors and how to specify them (Metrics Module section)
* Clarified info on:
    * storage tiers and added the property druid.server.priority (Storage Node Module section)
    * segment cache : where historical nodes store data in disk cache
    * druid.query.chunkPeriod
* Removed druid.db.connector.pollDuration
* Fixed definition of druid.selectors.indexing.serviceName and moved to discovery section
minor edit to Metrics Module section
Merge branch 'master' into igalDruid
Merge pull request #485 from metamx/igalDruid

Igal druid