Update EhCache configuration to use pooled resources for cache sizing

With EhCache 2.5.0 functionality was introduced to allow caches to be sized using bytes as an alternative to using the number of elements. One can also define the overall heap space that EhCache will use as well as what percentage of the overall cache's heap each named cache will use. See http://ehcache.org/documentation/configuration/cache-size#pooled-resources

I would like to update Shindig to use this by default, as I think it should be the recommended method for configuring EhCache's use in Shindig out-of-the-box.

As part of the deliverables for this JIRA, I will be updating and maintaining portions of the wiki: https://cwiki.apache.org/confluence/display/SHINDIG/Index#Index-CachinginShindig