[WIP] Use bootstrap-sass instead of the static bootstrap.css + general cleanups

**Do not merge or small kittens will die!** Should close #28. Also refactor/clean up the code as it seems to be quite a mess.

## ToDo

- [ ] refactor/clean up home
- [ ] refactor/clean up about
- [ ] refactor/clean up get involved
- [ ] fix footer styling
- [ ] fix responsive-css errors
- [ ] replace "all" icons, they should look similar...
- [ ] make the content more readable, maybe split into multiple subpages