Release 6

Final release for the duration of the course DAT-255.

Make sure that before merging;
* All documentation (meetings, reviews, developer documentation, user guides, etc.) is in the docs folder and up to date. (Wiki pages must be converted to pdf).
* The code is cleaned up, both using the formatting tool and that obsolete comments (such as fixed TODOs and uncommented code) are removed.
* The .apk is exported again with the newest code.

This branch should also be merged back into dev.