Allow basic list operations

[unsegnor]

Examples:
I would like to add a new value to a list without getting the entire list
So if I want to add a new room to my house I can just do "house.add('rooms', room)"
and the room is added to the list of rooms in the house

Rules:
Allow list operations (add and remove) directly over the property instead of getting the array operating and then setting it again.

Doubts:

Developer Notes:
This could require a different kind of representation of the arrays the state. This also allows us to improve the performance.

[unsegnor]

The 'add' method was already implemented on version 2.1.0