Implement a mechanism for deleting/resetting cached data in Minimongo

[npvn]

Currently once data is loaded into Minimongo, there isn't a mechanism to reset it. Calling subHandle.stop() will in fact only trigger the registered onStop callback (if any).

We need to evaluate whether this feature is really necessary, and whether it is feasible to reliably track and reset documents retrieved via different Methods.

Note: Most of the time it should be enough to keep data up-to-date by calling a data fetching Method on route load and set an appropriate cache duration for it.