Directly use IModelHandler API for finding content type fixes #38

The previous API for getModelForRead() actually just internally delegates to the IModelHandler to load the content type.  With this API we are just calling the model handler directly to ask for the content type.

The problem was that the getModelForRead() when you load a really large file like a 23MB xml file, was creating all of the necessary jface dom adapters for rendering the XML file in the UI.  So it was doing way to much work and creating too many UI related objects that were never needed for simply looking at the content type.