Add freeze(obj) and unfreeze(obj) methods

[misko321]

The ngStorage by default watches for any changes of an added object, to update the localStorage. In some cases however (like this one: https://stackoverflow.com/questions/32856511/localstorage-value-got-change-with-fabric-js/32966097#32966097) it would be very helpful to disable the automatic updates by some sort of freeze(obj) method which would prevent the object from further modifications. Optionally, unfreeze(obj) method in turn would reenable the watch, and start syncing the object and its localStorage representation again.

[btm1]

+1 yes plz

[rhclayto]

Yes, also a +1 from me. This would greatly expand the flexibility of this essential module.

[TomekSzymanski]

+1

[georgski]

+1