Pages: Add options to select custom search fields

[mahagr]

It would be nice to be able to override the default search and search by content for example.

The logic already exists to do this, we just need to update both js and task to take in the custom set of fields.

[w00fz]

Tell me about the logic that already exists.

[mahagr]

I mean that flex objects already support custom searches to any field by just providing an array of the fields to the search() method. So we just need to add the UI and pass the search fields to the method in the controller.