Add support for editing scheduled dates without editing event.

[joedolson]

The current mechanism for editing an individual date in a recurring event opens a full editor for the event, and the edit process splits the event to allow for custom content. However, if the only change desired is to modify a recurring date, that should be achievable without splitting the event.

Change 'Edit' to 'Edit Event' and 'Edit Date'.

Execute 'Edit Date' as a dynamic update to just the date in the occurrence table.