Override improvements

We've made two improvements to link availability overrides:

1. You can now choose to apply a link overrides to all attendees or to a specific attendee. Previously, we always applied all link overrides to all attendees (and there was no explicit all attendees option), which lead to unexpected results with complex links that include multiple attendees.

2. You can now click on individual overrides to modify or delete them. Previously, you could not edit an existing override and you have to highlight override you wish to delete and click "Clear" to remove them.

We hope these improvements make the task of adjusting availability a lot smoother!