Resolve "web interface for keama"

This MR adds a lot of new functionality:

• web interface, written in python/Flask. See web/ directory.
• basic tests for testing the functionality. See section about testing in doc/web.py.
• documentation for web. see doc/web.py.

This is a joint effort of @tomek (coding), @vicky (lots of text), @slawek (styling improvements, help with tests), @manu (health check and many suggestions).

Closes #13 (closed)