MSVC Warning cleanup, /WX (Werror), and misc. fixes

[Nopey]

• DEBUGMODE is now defined on MSVC debug builds
• VS_DEBUGGER_ENVIRONMENT now tells game where to find the resources and shaders, needed because build\resources is not next to build\Debug\openomf.exe (another solution I used previously was to copy the resources into build\Debug, but that's messy)
• Warnings are now either: silenced, treated as errors, and or fixed.

Enabling and fixing C4668 may be a bit silly, but I was feeling guilty about my habit of writing #if XYZ instead of #ifdef XYZ (where XYZ is maybe-defined, like __APPLE__)

implicit lossy conversions

The following two warnings are now be disabled, and are comparable to GCC's -Wconversion; -Wconversion is not enabled on master branch. Banning implicit lossy conversions is a good idea for another time, but fixing them will generate a lot of line diff noise.

C4244: implicit conversion, possible loss of data
C4267: implicit conversion from size_t, possible loss of data