Fix project to be Mono compatible (work in both MonoDevelop & Visual Studio)

[tcannonfodder]

I use OS X as my primary machine, so it's kind of a hassle that I have to boot up my PC any time I want to work on Telemachus. Other Mac developers might not have a good setup for running Visual Studio. We should tweak the solution to work in MonoDevelop and OS X/*NIX setups.

[Frank-Einstein]

I would need this too! I don't have Visual Studio, I only use MonoDevelop for KSP addons.
(I don't have enough disk space right now for installing Visual Studio...)

[AntiSol]

FYI I was able to open the .sln file in monodevelop on Linux and build as per the build instructions, worked fine and was pretty straightforward :)