Ask for confirmation before deleting something in teacheradmin

In the units view
Update install.rst
Do not show a button for creating a question or a pr assignment if there's already one of them created

The option of creating a peer review assignment or a question is not shown when
one of them already exists, as the classroom view does not handle KQs with both
a peer review and a question.
Use the weight in the teacher admin, instead of the normalized one
Merge pull request #32 from fid-jose/master

Allow creating only either a Question or a PR in a KQ
Add JS translations to the classroom view

They were being used but the lib wasn't being loaded
Remove useless console.log call
Merge remote-tracking branch 'upstream/master' into feature-openbadges