better diff for feed metadata comparison test
TW-30396 fix the guest auth link
make feed compatible with actual 2.6 version (add a number of @NotNull's to attributes)
TW-30395 fix tools order
added NuGet 2.6
added 2.6 to .NET build
include 2.6 tests
introduce nuget 2.5 plugin, share code
fix tests run for 2.5,
run tests for 2.6
TW-30001, TW-30228
TW-30229