Butter lets users create new, orphaned and useless slidedrive events

[banksJeremy]

Butter lets users add new events to the timeline by dropping them from the list of event types on the right.

Creating a new slidedrive event, unassociated with any slide in the document, is pointless and will probably break things.

We should address this somehow, either by disallowing the drops or doing something more useful.

[banksJeremy]

This might be getting ahead of ourselves, but maybe we should

1. allow new slides to be created like this, with some minimal default content
2. set .contenteditable = true on all sides, letting users edit them in-browser... albeit crudely.

We'd have to put this in the slidedrive plugin itself.