JSON-RPC

Changes made in this pull-request:

- jsonrpc api with all methods available from javascript-api
- added cors headers to jsonrpc
- separated libethrpc
- Javascript jsonrpc client, with the same interface as Javascript bindings in EthereumBrowser, so there is now possibility to run/debug code using eth object in Chrome/Firefox and other browsers
- here is a playground - https://github.com/debris/eth-client-example
- added async setters/getters for javascript properties
- tests for most of jsonrpc methods

* api is not yet unified with Go client api
I see a conflict with m_qweb being re-allocated within loadStarted. That is, when main is deallocated it will call ->clientDieing() on m_qweb. However, QWebThree instances which are implicitly deallocated will not have clientDieing() called on them.
Can m_qweb be reset between loads instead of reallocated each load? If not, can clientDieing be called when it's deallocated or via a QWebView callback?