Improvements of the agreement between SS Server and SS client for connectors.

Review and merge the branches refactor/context_script_on_client.

Top level issue: https://github.com/slipstream/SlipStream/issues/18

Related pull requests:
- https://github.com/slipstream/SlipStreamClient/pull/59
- https://github.com/slipstream/SlipStreamServer/pull/209