[SUGOI] Level select no longer assumes that games will always be linear

If a level is in-between two with the same header, it would previously create two headers with the same name. Now it groups all levels with the same header together.

Before:

After:

Previously, a header would only be visible if its first map was visible. Now it will show the header if you've visited any level under the header.

Before:

After:

EXE: srb2win_select-heading.exe