Feature Request: Ability to unmount collections and cleanup all local data

[obedm503]

Right now neither the SyncManager, Collection, nor the PersistenceAdapter have a way of getting destroyed and cleaned up.

This means that when a user logs in to an application, uses it, and logs out, a malicious attacker could inspect the console and get access to all the cached information. PersistenceAdapters have no way to unregister and clean up after themselves and possibly confidential information remains on the system.

I am requesting a destroy method on the SyncManager and Collection classes to clean up after themselves and call the underlying persistence adapters' unregister method. Then, persistence adapters would implement their specific clean-up logic.

[psicomante]

I just saw this issue after creating #960. My issue is basically the same and I wrote some code to propose a solution. I didn't start yet using SyncManager, so i don't know if Max is going towards same direction or not, but I could do a PR in case my solution could be a nice idea to add.