WIP - 0.6.8 - Hammering the install and packaging process

A bunch of bugfixes in here:

 - Installer should only run for the latest release, not every release it finds
 - The output from `CreateReleasePackage` now lists three files - these are displayed correctly
    - the full package
    - the base package for the delta package (currently wrong, should be previous release instead of latest release)
    - the delta package
 - tabs tidied up to spaces now

TODO:

 - [ ] tracing around `InstallManager` and `UpdateManager` to highlight (and then fix) bugs raised by users [here](https://github.com/github/Shimmer/issues/44)