Complete the Shimmer -> Squirrel transition

TODO:

 - [x] publish point releases of Squirrel.Core, Squirrel.Client and Squirrel.WixUiClient
 - [ ] see what @paulcbetts comes back with in terms of being able to use the `Squirrel` - fallback is Squirrel.Windows
 - [ ] publish deprecated packages for Shimmer, Shimmer.Core, Shimmer.Client and Shimmer.WixUiClient which point to the new packages