Fix event type and parameter type confusion

I'm not sure if this is really the best way to do event types (should it
just be a completely static enum in evoral, or completely dynamic and
provided by the type map, or a mix like currently?), but previously the
event type was frequently set to either total garbage, or parameter
types, which are a different thing.

This fixes all those cases, and makes Evoral::EventType an enum so the
compiler will warn about implicit conversions from int.

libs/evoral/src/Note.cpp

@@ -30,9 +30,8 @@ namespace Evoral {
 
 template<typename Time>
 Note<Time>::Note(uint8_t chan, Time t, Time l, uint8_t n, uint8_t v)
-	// FIXME: types?
-	: _on_event (0xDE, t, 3, NULL, true)
-	, _off_event (0xAD, t + l, 3, NULL, true)
+	: _on_event (MIDI_EVENT, t, 3, NULL, true)
+	, _off_event (MIDI_EVENT, t + l, 3, NULL, true)
 {
 	assert(chan < 16);