Add `email` action

[tfeldmann]

Adds an action to send a file as an email. One can use template variables in subject and body. As the simulation output for this action does not fit into a single line the action base class is extended to support multiline output.

[tfeldmann]

Although this is working some decisions are still open:

• Password should not be in the config file. Load from environment variables?
• sim / run output?
• Global settings dict with defaults in the config file? Otherwise you repeat parameters a lot.
• Allow template variables in the other parameters?

Also missing:

• Documentation
• A good __str__