Improvments to ResrcIt support

Small (but thoughtful) tweaks to the `ResrcIt` class to:
- Allow existing operations to be passed in on `initialize`
- Ensure that when instances are cloned/duped the operations array is a clone of the original's array, not a reference

Also changes `ImageHelper#resrcit_url` to allow it to accept an existing `ResrcIt` instance instead of a URL string.