Only allow one running instance on a machine

This fixes #15, though it would be nice to show the settings on the
running instance or do something visible so it's clear that at least
something is happening. That will need to wait for #16 though, I haven't
figured out a way to use broadcast messages (the app doesn't seem to
always have a window object we can hook)
use explicit class name

this resolves ambiguity given the internal UI class with the same name
move windows API to internal class
remove unused namespaces
Merge pull request #17 from DataSplice/single-app-instance

Single app instance