[IMPROVED] jsonRPC Error Handling with CURL

* [ADDED] Use curl instead of fopen
* [ADDED] Error handling for various connection issues
* [MOVED] jsonRPC library into lib folder
* [UPDATED] Pools page for proper RPC errors with caching enabled

It's using the base RPC class but modified to support CURL. Simplified
some code since we won't need those features. Should make maintaining
that code a whole lot easier.

Fixes #1343 once merged.