Resolve "Add text to edit booking page about moving a booking"

What does this MR do?

Add a message about moving a slot and about no bookings being made

Also fixes an issue with edits being broken (lack of constructor).

Closes #207 (closed)

Does this MR meet the acceptance criteria?

• I have added tests to validate the new functionality.
• I have updated the documentation accordingly.
• I have added translations for all new client-side text.
• I have updated the changelog accordingly.