Update CONTRIBUTING.md

Add a note about pull requests to be done against dev branch
Update CONTRIBUTING.md
Initial rtl detection
Misuse of jquery object - use DOM object instead
Add initial rtl styles

We swap out images for the flipped versions, and modify any css
styles with hard-coded handedness.
Some playful rtl style fixes
Support RTL for sliders.

(Requires some additional data in javascript.)
Ensure LTR text for help menu (no translations yet anyway)
Merge pull request #315 from chowey/i18n

Add RTL support - fixes #310