Add no transform

Status: **Consider merging**

Reviewers: **@johnboxall @jansepar**
Linked PRs: **https://github.com/mobify/imageresize/pull/47**

## Changes
- Adds support for "no-transform" format, whihc will cause resizing options (height/width) to be dropped

## How to test-drive this PR
- Take a look at the tests, run 'em
- Try using it with a project, by pointing its bower dependencies this-a-way
@noahadams seems like we've doubled up the logic here? We can probably remove this one and just rely on what's below?