Implement frontend for dialects in control panel

[robinharms]

The branch 0.43 introduces two endpoints for installing/removing dialects. It's added on the meeting rest endpoint, detail view with action install_dialect or remove_dialect

• Warn when installing or removing a dialect - it's not a small thing and users won't see the result until they reolad.
• It's only possible to change dialect when the meeting is upcoming.
• When removing, try to explain the result of removing in frontend. Perhaps some kind of other check. (I love the "Warning, unexpected and bad things happen if you don't read this" in github)