getDataFromDom -> getModelFromDom

Following on from getDomFromModel, this returns a document model
instead of element linear data. The only instance that hasn't been
replaced is in rich paste, where we need to sanitize the converted
data before constructing the document model.

This should be cleaned up in a later commit.

Change-Id: I37a2b641632af2cb515e3409deed5cd1fa358af5