Mass refactor 'unsigned int' ==> 'int'

[KevinHake]

Tried to keep this one only unsigned to int changes. Touches a ton of files. I left libs alone, along with a few things like network_util.

[KevinHake]

All the appveyor errors were for spdlog. I don't think this commit touched anything in libs at all, let alone spdlog so I'm not sure what's going on. Everything built for me fine locally, tests passed, the game ran.

C:\projects\rwe\libs\spdlog\include\spdlog\fmt\bundled\format.h(801,1): error C2660: 'std::allocator::allocate': function does not take 2 arguments [C:\projects\rwe\build\librwe.vcxproj]

One difference I have locally is that my spdlog.vcxproj has PlatformToolset set to v142 instead of v140, since I don't have the 140 toolchain installed (I'm using VS2019)