Calculate padding and pivot length based on Font Metrics

The pivot indicator length can set from the FontMetrics.bottom - more info can be found here http://evendanan.net/2011/12/Font-Metrics-in-Java-OR-How-the-hell-Should-I-Position-This-Font/

While the top and bottom padding can be determined by multiply the pivot indicator length by 2 which should make the indicator line never overlapping the pivot letter

The xml attributes padding, paddingTop, and paddingBottom will be additional padding for the calculated padding in the above statement.

This also removes the chrome padding that was added for the circle clipping in the old pivot indicator.

A preview: http://www.youtube.com/watch?v=rossRSokq4Y