Rewrite Movable and MultiSelect components with support for Backbone.Collection

[vicentemundim]

We currently use simple arrays for Movable and thus MultiSelect. It would be great to use Backbone.Collection for the Movable component, since it has support for using a comparator, which is basically the functionality we need in Movable.

We have to be aware of performance issues, since we may be throwing some overhead onto this lists. An automated performance test would be of great value here.

An advantage of using Backbone.Collection and Backbone.Model instead of using pure arrays and Objects would be the possibility to listen to specific model events, and bind them to specific views.