Use enums for music tracks

This adds an anonymous enum for music tracks and replaces all calls to
music.play and music.niceplay that use integer literals. Additionally,
this is also done for integer literals for cl.levmusic (except 0) and
music.currentsong where appropriate, but _not_ the music areamap because
that would not make it look very aesthetically pleasing in the code.

This is not a named enum (that can be used for strict typechecking)
because music track IDs are essentially part of the API of the game -
almost every custom level uses these numbers. This is just to make the
source code more readable without needing a comment to denote what
number is what track.

desktop_version/src/Editor.cpp

@@ -299,49 +299,49 @@ static void editormenurender(int tr, int tg, int tb)
         case 0:
             songname = loc::gettext("No background music");
             break;
-        case 1:
+        case Music_PUSHINGONWARDS:
             songname = loc::gettext("1: Pushing Onwards");
             break;
-        case 2:
+        case Music_POSITIVEFORCE:
             songname = loc::gettext("2: Positive Force");
             break;
-        case 3:
+        case Music_POTENTIALFORANYTHING:
             songname = loc::gettext("3: Potential for Anything");
             break;
-        case 4:
+        case Music_PASSIONFOREXPLORING:
             songname = loc::gettext("4: Passion for Exploring");
             break;
-        case 5:
+        case Music_PAUSE:
             songname = loc::gettext("N/A: Pause");
             break;
-        case 6:
+        case Music_PRESENTINGVVVVVV:
             songname = loc::gettext("5: Presenting VVVVVV");
             break;
-        case 7:
+        case Music_PLENARY:
             songname = loc::gettext("N/A: Plenary");
             break;
-        case 8:
+        case Music_PREDESTINEDFATE:
             songname = loc::gettext("6: Predestined Fate");
             break;
-        case 9:
+        case Music_POSITIVEFORCEREVERSED:
             songname = loc::gettext("N/A: ecroF evitisoP");
             break;
-        case 10:
+        case Music_POPULARPOTPOURRI:
             songname = loc::gettext("7: Popular Potpourri");
             break;
-        case 11:
+        case Music_PIPEDREAM:
             songname = loc::gettext("8: Pipe Dream");
             break;
-        case 12:
+        case Music_PRESSURECOOKER:
             songname = loc::gettext("9: Pressure Cooker");
             break;
-        case 13:
+        case Music_PACEDENERGY:
             songname = loc::gettext("10: Paced Energy");
             break;
-        case 14:
+        case Music_PIERCINGTHESKY:
             songname = loc::gettext("11: Piercing the Sky");
             break;
-        case 15:
+        case Music_PREDESTINEDFATEREMIX:
             songname = loc::gettext("N/A: Predestined Fate Remix");
             break;
         default:
@@ -1909,7 +1909,7 @@ void editorlogic(void)
         graphics.titlebg.colstate = 10;
         map.nexttowercolour();
         game.quittomenu();
-        music.play(6); //should be before game.quittomenu()
+        music.play(Music_PRESENTINGVVVVVV); // should be before game.quittomenu()
     }
 }