Update settings and save features

Add more to the save feature including saving the icons
associated with each diff tool
Remove "magic" strings and update LoadAll()

Add defined strings for all elements and attributes stored
in XML
Implement some of the LoadAll() settings method.
Add full load and save features

LoadAll and SaveAll now save all attributes of all Diff Tools
currently in memory. Basic task complete.
Refactoring in order, and perhaps consider using Google Protocol
Buffers instead of XML.