question bank button

- added button in examgroup-view for switching into question bank
- added button in exam-view to open question bank in a new window
edit questions from exam view
2 bugs removed

- choice-categories were not shown properly
- rebuild of shuffle-values were not correct
get questions of courses by having capability

capability is  "moodle/course:changeshortname"
open question bugfix

- link was blocked by selectable-property
Merge remote-tracking branch 'compl3te/uni_leipzig' into uni_leipzig