Uninstall should actually uninstall

Little things:

 - Fixed up some bugs with how WiX triggers uninstall
   - occurs in background, so no dispatcher present
   - don't show the ViewModel when in background
 - Check the Win32 exception when MOVEFILE_DELAY_UNTIL_REBOOT fails
 - `Create-Release` cleans up the test logs
 - testing our package detection code

Bigger things:

 - the uninstall step should not throw an exception about incorrectly disposing resources
 - running a newer installer should tidy up the old installer (from Windows mostly)

TODO:

 - [x] when an old installer runs and uninstalls itself, do not clobber later versions (i.e make the test pass)
 - [x] some issue with not disposing UpdateManager properly when running the second installer
 - [x] investigate why the uninstall steps are throwing a FileNotFoundException (race condition? awesome!)
 - [x] get to the bottom of why the uninstall seems to succeed but doesn't