Tiny refactoring and fixes

- moved "#include <cryptopp/sha.h>" from headers to .cpp files. This reduced warning spam during compilation a bit and marginally improved compile time.
- the "!gVoiceVolume > 0" expression made a cast from double to bool, which definitely wasn't intended. The mistake went unnoticed because the end result was the same.
- one of the expressions in SelectionScreen.cpp was checked two times in a row. I don't know what was the reasoning about it, but I assumed there was nothing else supposed to be there so I removed it.

I'm not sure why git shows some lines as being changed, is that related to line endings? I never had an issue with them before.