Add a field for the webinar URL to events

[oliverklee]

• [x] locallang (in separate PR)
• [x] model
• [x] repo tests (red)
• [x] SQL
• [x] TCA for single events and dates
  • [x] exclude
  • [x] type (limited)
  • [x] conditional
• [x] repo tests green
• [x] manual tests in 10 and 11
• [x] DE translation
• [x] update 10 and 11 installations: DB dump and labels
• [x] update maschinenrichtilinie: labels, DB dump, permissions