CacheProxy refactored, cleaned up

* CacheProxy refactored into three classes. 
* CacheProxy related checkstyle issues fixed. 
* Code duplicates removed.
* LoadAll async behavior is fixed.
* ICache doc improved
* ICache API addition, two async methods
Very dangerous to catch a throwable. Catching exceptions is one thing, but catching throwables is ware more dangerous. It could be an OOME you are ignoring.