Update Javadocs for plugin configuration.

This makes the Javadocs comply with changes done in https://github.com/Netflix/Hystrix/commit/bfb66969baaa38a16e9dfce872e6ad6a4012d443
Remove TODOs made invalid by HystrixPlugin changes

Plugins can not be modified after registration so caching is okay.
Change Throwable to Exception

Generally not good practice to be catching Throwable so changing to Exception.
Remove unused code.
jettyRun support for running webapps via gradle
HystrixCommand Execution Hooks

Execution Hooks via Plugin https://github.com/Netflix/Hystrix/issues/10
ExecutionHook: Change onSuccess to onComplete

I think onComplete is clearer since the response can be either from run() or getFallback()
Make servlet-api a provided dependency
Merge pull request #73 from fkjellberg/servlet-api-provided

Make servlet-api a provided dependency
Additional javadocs for ExecutionHook/EventNotifier
Merge pull request #71 from benjchristensen/execution-hooks

HystrixCommand Execution Hooks https://github.com/Netflix/Hystrix/issues/10
Property to disable percentile calculations https://github.com/Netflix/Hystrix/issues/15

The property actually already existed from earlier work I did when opensourcing and was already preventing 'addValue' from being called but I've changed it now to be part of the HystrixRollingPercentile itself.

This makes it so anything that calls it, including Metrics polling won't trigger the internal logic and when disabled it will just do no-op and return -1 for values.
Property to disable fallbacks https://github.com/Netflix/Hystrix/issues/69
Merge pull request #76 from benjchristensen/properties

New Properties (fallbacks and rolling percentile)
Bumping up the connection quota for the dash proxy stream servlet
Flushing the buffer on line feeds
Merge pull request #77 from opuneet/FixProxyStreamFlushBug

Fix proxy stream flush bug
Version 1.2.0-SNAPSHOT
Gradle Release Plugin - pre tag commit:  'hystrix-1.2.0'.
Gradle Release Plugin - new version commit:  'hystrix-1.2.1-SNAPSHOT'.