Active Learning

[RandomDefaultUser]

Adds active learning to MALA. Implementation originally done by @kyledmiller. I used the diff between https://github.com/kyledmiller/kdm_mala and the last point of divergence in the main MALA repository to create this branch. This was necessary because in between both branches lots of the MALA code had been reformatted.
The regular functionality of MALA has not been altered by this PR.

TO-DOs to merge this PR:

• Test that new functionality is properly working
• Create a test for this new functionality
• Create an example for this new functionality
• Document changes
• There seems to be a small increase in processing time when starting a regular training (without active learning) after adding the active learning code; find out what causes it