Freeze buttons on UI
Add tests to check for freeze access

Only available to staff users
Add API endpoints for UI freeze (cf. #141)
Http for freeze UI (cf #141)
Freezes Http / JS
Freeze / unfreeze from UI (fix #141)

Lacks a few adjustments.
Streamline UI (freeze buttons disappears). Cf #141
Merge pull request #144 from Neamar/ui-freeze

Ui freeze