Refactor, updated readme, colors+style to closer match Sparrow

[rnystrom]

• Changed the color preferences for gradients and borders to match Sparrow. Here is the example I used.
• Shadow opacity and sizes to match Sparrow.
• Shadow changed to white and radius 0 when active to give a bezel appearance.
• Refactor toggle code to be more DRY
• Static init method so it can't be overridden
• Added -init and -initWithCoder: for more options

Had fun with this! I almost opened Pandora's box to do some drawing for a gradient border. They need to update the API to make this easier instead of having to do EO clipping w/ 2 paths. Didn't feel like going that far this morning.

[ocrickard]

This is seriously awesome. Thanks so much Ryan!