Figure out how to manage stacked notes

[Thesola10]

A common practice on osu!classic is to stack several notes on the same coordinates. Internally, they share the exact same location, but the game offsets them so as to keep them readable.

On osu!DIVA, leaving the notes on top of each other makes them hard to read, so here are two proposals to deal with this:

• We implement the offset like osu!classic does, so as to keep the notes readable, or...
• When several notes share the same position on a converted beatmap, force them to use the same button, as is common on Project DIVA maps.

[Thesola10]

For long cascades where several kinds of buttons are used, we could try to separate them clearly around the center point, sorted by type (triangle = north, circle = east, square = west, cross = south), to emulate how official DIVA maps manage repeated inputs