Auto-transfer infos

See the docstring for Component.create_connector for details on how it works.

I think this is a nice usability enhancement. The TimeTrigger component nicely shows how it can simplify the code for transferring metadata. Although it is still relatively complicated how the rules are constructed there, as the component is flexible regarding in which direction to transfer/where to take from. But all the complicated stuff in _connect is automated.

Fixes #73 (closed)