Project seperation.

[KevinJump]

Finally as part of phase 5 - better structure #218

Split into bits, so we can manage things easier.

• Core - Core migration control
• Client - UI, so the app_plugins and controllers
• Migrations - Where the migrators live,. this is where most people will need to put code.
• Tests - tests

uSync.Migrations is the main nuget package, it has dependencies on the rest.