Clean up (es6 optimizations, memory leak on listeners)

[mindflowgo]

Added a backward compatible feature enhancement:

• viewport resize bars so we adjust it on the image: pass in "resizeBars: true" in the options.
• added enableRotate option: adds rotate buttons beside zoom bar to rotate 90, 180, 270 degrees.
• get() method: ability to get crop rectangle & transform/viewport to restore viewport
• preset parameter on bind(): ability to restore picture to location it was at before in viewport

Scope of changes:

• core logic kept same, some cleanup of es6, listener cleanup, goal to keep changes intuitive and non-breaking on code base
• transform logic consolidated into #preserveTransform()
• built out resize handle bars
• buit out rotation logic (rotating image canvas to minimize logic changes)
• adjusted demo code to showcase new abilities.

Thanks for the awesome project!