Add simple Task<T> for background loading in the menu.
Use Task<T> for loading routes, activities, paths and consists.
Paths and consists now show pretty names instead of filenames.
PATFile now loads file, start and end strings.
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@556 a9f3cfff-6c41-7446-b0ca-052bd761e6eb