[REF] Don't use separate blueprint for shorturls

Not necessary anymore now that we can ignore url_prefix
[MIN] Add event management blueprint stub
[IMP] Unify shorturl validation

- use same rules in all cases (ajax and classic form)
- always validate the url client-side, too
[IMP] Pretty URLs: Event mgmt: general, contrib types
[IMP] Pretty URLs: alarms
[IMP] Pretty URLs: cloning
[IMP] Pretty URLs: lock/unlock