Add hex color display and entry support

Added an EditText to the dialog that displays the hex value of the currently selected color, with the alpha part of the hex value being shown only when the alpha slider is enabled. The EditText also allows users to enter their own hex value in. When an invalid hex value is entered, the text turns red. When a valid hex value is entered, the selector snaps to the color defined by the entered hex value.

![device-2013-05-21-185357](https://f.cloud.github.com/assets/1767319/546152/df1f59a6-c282-11e2-9f01-8e89cee69e48.png)