msvc: resolve all warnings in Core.

Note: vs14 will support empty macro parameter as used by MMIO.
msvc: resolve all warnings in VideoCommon.
msvc: resolve all warnings in VideoBackends/Software.
msvc: resolve all warnings in VideoBackends/OGL.
msvc: resolve all warnings in DolphinWX.

Also, bring WiiSaveCrypted closer to modern dolphin coding style.
msvc: enable compiler warnings as errors.