New way to detect a Restangularized element

Actually: if a plain object has a key `one` or `all`, it will be detected as Restangularized and those keys will be removed, which is wrong.

Added a new specific key `restangularized` that I set to `true` when the element is restangularized and use it for detection. I hope I didn't forget any place where to set this flag.
You should set this field in the call of `restangularizeBase` I think instead of here.