#37 Refactored exercise card + fixed duplicate hero key error

[jorre127]

• Did a refactor of the exercise card tho make the code a little shorter and cleaner and fix some bugs.
• Fixed the issue of duplicate hero keys on the floating action button

I changed quite a lot of the logic (the exercise card was 300 lines now 200) so be sure to check if nothing got broken during the refactor. I already checked and everything seems fine, but you can never be too sure.

closes #37

[jorre127]

I agree, didn't do it in this PR because I was already changing so much outside the scope of the ticket (this was supposed to be just a Bugfix) but I think preferably we should just make a separate issue to fix all the analyser errors like unused imports/code etc. So we can fix them immediately all at once, instead of gradually.

[KalleHallden]

Nice work, @jorre127 could you check this again. After I merged the #55 there seems to be a few conflicts.