Enums for TapNoteType, TapNoteSubType, and TapNoteSource

I intend to make additional useful information available on judgments,
such as TapNoteType and TapNoteSubType( for hold judgments ).

I am submitting this part as a separate pull request because it is more
generally applicable to anything TapNote related.

src/ScreenHowToPlay.cpp

@@ -221,7 +221,7 @@ void ScreenHowToPlay::Step()
 	{
 		const int iNumTracks = m_NoteData.GetNumTracks();
 		for( int k=0; k<iNumTracks; k++ )
-			if( m_NoteData.GetTapNote(k, iNoteRow).type == TapNote::tap )
+			if( m_NoteData.GetTapNote(k, iNoteRow).type == TapNoteType_Tap )
 				iStep |= 1 << k;
 
 		switch( iStep )