Adding button accessors and holo text colors to button text

I needed access to the buttons in order to disable/enable them.  For example, if an EditText length is 0, disable the positive button.  The buttons will be null until the view is created so they shouldn't be accessed before onVewCreated.  Also changed the button text color to use the standard holo light/dark text colors so the color would be different if the button was disabled.  These were pulled in from AOSP.

I changed gradle to target 18 as well.