fetch ICSharpCode.SharpZipLib from nuget
fetch MaxMind.GeoIP2 from nuget
fetch SharpFont from nuget
fetch NUnit 2 from nuget
fetch SDL2 (native Windows DLL) from nuget
fetch Mono.Nat from nuget
Merge pull request #7197 from Mailaender/nuget-thirdparty

Cleaned most of the thirdparty folder from foreign binaries
Update INSTALL.md

try to explain the changes from #7190 and #7197