Added isTablet and upgraded to Spring Mobile 1.1.0M1

Upgraded to Spring Mobile 1.1.0M1 and wurfl 1.3.1.1.
Also upgraded to grails 2.1.0

The new spring mobile added a function to detect tablets. We need this
for a proejct we are working on, so decided to add it.

This plugin adds a withTablet dynamic method to the controllers.