Change radius using scale and multiple showcase views

Added the ShowcaseViews, as per Blundell's suggestion, which makes use of the builder.

Fixed the builder to actually have a build method!

Added showcase chaining to the sample demo activity.

Added the ability to be able to change the scale of the showcase circle. This is radius of the circle, so you can make it as small or big as you like.

Antialias'd the circle to make it a little smoother.