PR to master: Periodic Relaxation Feature

[Short summary of feature]

Currently, the periodic relaxation branch contains multiple features. In a first step, we integrate only the periodic relaxation feature in to master. Commits: 090be140 20fe000c 5f058656 9c5ae611 4173bab6 467c6026 571fc71d bc744bab e0076648 d78c8e61 7c5fed88 ee65fe08 b5e7f6f6

Next steps:

• Create merge request for issue (after merging !50 (merged))
• Cherry-pick commits into merge request branch (support: @brgerhar, @mspinola)
• Add tests
• Review code (see plan in wiki)