Loading MainWindow as an extern

Trying to tie the model creation stuff to the tree view on the main
window.  Groundwork is done.
Well... that didn't work

My example code was far too complex and dependant on one UI element,
could not be applied to other items.  Starting over.
Working better now

The method for getting data into the model isn't ideal but it goes in at
least.
Minor changes

Selected mech is automatically mech at index 0 for "optimize selected
mech
Good changes
Armour reporting works... sort of.
Merge pull request #3 from galorin/TreeModel

Pull in first MechTree version