several improvements and optimizations

Account
* lazy and full are correctly passed
* _parse_json_data() added to parse json
Block
* lazy and full are correctly passed
* empty operations are handled
* op_statistics improved
Blockchain
* virtual ops and ops statistics are seperatly calculated
Comment
* _parse_json_data() added to parse dates and amounts
* author_reputation is parsed to int
* lazy and full are correctly passed
Vote
* lazy and full are correctly passed
* _parse_json_data added to parse date and rshares and reputation
* vote.time is a datetime object
* json() returns the original string
Witness
* lazy and full are correctly passed
GrapheneRPC
* time_limit removed, as it supresses KeyboardInterrupt
* ws.settimeout() is set for websocket
* WebSocketTimeoutException  handling added
Unit tests
* test_account fixed
* test_time_limit removed from test_steemnoderpc
* checks added to test_blockchain_batch