DATAREDIS-206 - Add support for TIME operation.

Enhanced RedisServerCommands to reflect time operation and added empty implementation to recent RedisConnection abstractions.
Added implementation of time() for Srp, Jedis, Lettuce (emulated via eval).
Added UnsupportedOperation of time() JRedis since it doesn't support time command or sending scripts or sending raw commands via the underlying connection.
Added implementation for DefaultStringRedisConnection to delegate time() operation to native connection.
Added integration test to abstract base class. Ignored the test for those connections not supporting time command.

Original pull request: #34