Clean up .csproj files to reference KSPRoot

[periodically-makes-puns]

Currently Telecom.csproj references a mishmash of 3 separate KSP installations. This changes the reference syntax to how RP-1 handles references in its csproj, which should hopefully help enable build automation.

There are two issues:

• We still have an unstated Principia dependency for certain bits of UI code.
• TelecomTests does not run unless all references are present in the folder where it runs. By default, this manifests as a failure to load RealAntennas; however it will not properly function until all references are in the bin/Release folder.