Add Backbone.js

Backbone.js v1.0.0 added as a submodule
Add twitter bootstrap

Twitter bootstrap added as a submodule at v2.3.2
Add less.js
Peg less.js to v1.4.2
Less.js 1.4.1

Less.js v1.4.1 is actually the stable version today, updated the submodule to point to it