Allow only dot notation on state access, remove array

We have decided to remove the array notation for state tree path access. This is primary to decrease complexity. With ES6 template literals and join it is relatively straightforward to turn any array into a string or combine strings directly.

If you have a good reason to keep it, please list it here.

• Add deprecation for array access

So for example instead of state.get(['app', 'users', userID]) you will now need to do state.get(app.users.${userID})

[edgesoft]

Think we should support both but have dot notation in all docs.

[christianalfoni]

We are doing this now, closing it 😃