added save_quietly method on Model

[JarriqTheTechie]

This method calls the save method on a model without firing the saved & saving observer events. Saved/Saving are toggled back on once save_quietly has been ran.

Instead of calling:

User().save(...)

you can use this:

User.save_quietly(...)

[JarriqTheTechie]

@josephmancuso / @girardinsamuel please review.