Add a sortFilter by default

By default we use the default JS sort function, by I recommand to use the underscoreJS one with the example I give
Add a "data" field to have the filter inside the select2 element, it's more efficient on small collections

This data field must be use on small collection of objects.

With this function, to give to the select2 element an array of objects and the select2 apply the search on the "text" field of each object in the array.

The text field compared is the one calculated by the "toText" function
Merge pull request #3 from JulienBourgain/addSomeFeatures

Add some features (grunt errors will be fix on the next commit