Demos: backbone-requirejs: Rewrite reference to jQM as a named module definition which depends on the actual jQM.
Gruntfile.js: Create subtask for backbone demo, reusing code that replaces references to the combined CSS, fixing path to core, and replacing conten of script that includes jQM with a named AMD module definition that depends on jQM. Fixes #6615 - Backbone requirejs demo is broken