This functionality should be merged into the DocumentTimerManager,
which itself should run the different document idle tasks via
seperate jobs instead of a single idle, if they don't depend on
each other.

To implement a non-busy, suspendable Idle, this adds an AutoIdle
class, which is automatically re-scheduled after being processed.

It also adds a SwDocIdle, which isn't ready to schedule for busy
documents.

Change-Id: I185137ed3423ecaae0f7edb39018d26c4244d359