Upgrade UI to Storyboard for Demo, Add Unit Tests to Demo, Add Color Mixer to Demo, Update ReadMe

Replace .xib file with .storyboard file and all UIViewController
subclasses updated. Add Unit tests to Demo app as XCTest. Add new tab
to Demo App called schemes which allows user to mix an RGB color and
see color schemes generated in realtime. Update ReadMe with new
screenshots.
Merge pull request #13 from craigwalton/master

Upgrade UI to Storyboard for Demo, Add Unit Tests to Demo, Add Color Mixer to Demo, Add colorWithRGBADict: Constructor