Changed Fury to use workspaces rather than load files.

Using the new interface component should ensure that the files have already been loaded
and therefore they should already be available to the algorithm when Fury is
run.

Refs #7681
Merge branch 'feature/7681_new_mantid_widget' of github.com:mantidproject/mantid into feature/7681_new_mantid_widget
Added fall back load statement just in case the user manages remove the workspace.

Refs #7681