0.6.8 - The One Where We Test Updating

Resolves #56 

Example:

![screen shot 2013-08-30 at 3 38 02 pm](https://f.cloud.github.com/assets/359239/1055382/67224ffa-1136-11e3-92e6-b35e04f5806b.png)

Done

 - delta packages now use the previous full release as a base package (not the latest full release)
 - tidied up the output from CreateReleasePackage (it will generate the full release and *maybe* the delta release filenames
 - added  a test to ensure no-one passes in a newer version as a baseline package

TODO:

 - [ ] get logging into UpdateManager
 - [ ] test real delta updates without having
 - [ ] document how delta packages work
 - [ ] (not really related) TestApp's commands are not respecting the CanExecute behaviour