Code cleanup, reduce warnings, fix proxy signatures

[Jand42]

Targets:

• reduce/eliminate Paket/Nuget warnings, update dependencies
• eliminate code warnings except where expected (directly testing that compiler warning is raised, or skipped tests for not-yet-implemented language features)

Improvement:

• Use FCS/Roslyn for proxy signature verification instead of Reflection if possible

Fixes:

• Valid proxy signature mismatches can be hiding, these should be fixed and tests added