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
Yes, owned() are keys+identities. I dont know if it is correct. It is the same as in develop [branch](https://github.com/ethereum/cpp-ethereum/blob/develop/alethzero/MainWin.cpp#L199)