Add functionality to generate KSP assembly attributes

[drewcassidy]

Adds targets enabled by the following properties:

GenerateKSPAssemblyAttribute

If set to true, automatically generates the KSPAssembly for your assembly from the Version property.

GenerateKSPAssemblyDependencyAttributes

If set to true, automatically generates KSPAssemblyDependency attributes for each dependency. Dependencies should have either the CKANIdentifier metadata or KSPAssemblyName metadata. Versions can be supplied with CKANVersion or KSPAssemblyVersion.

Also fixed up the CKAN install stuff so it only runs when absolutely necessary

Up for Bikeshedding:

• Should any of these be opt-out instead of opt-in?

[drewcassidy]

Changed my mind, MinVer is actually perfect to use and we don't have to reinvent the wheel. Ignore the branch name, im not renaming it