Delay entering replica until editing

[isglass]

Today we render incoming data first, then enter it into the replica and start calculations. Suggest adding a config to delay that until:

• User starts editing (dragging, resizing etc)
• Some API is called, eg. project.startCalculations(). Possibly only this case, since that is what the client requires (a button to enter edit mode)

The UI would display tasks and allow scrolling without calculations being performed.

Pitfalls: Engine sets up buckets (assignments, dependencies etc). That would have to be done separately without the engine, to latter be replaced by the engine. Otherwise dependency lines and resource avatars wont render