Super Gravitron #define

[AllyTally]

Changes:

As requested in #832, this adds a define for Super Gravitron. Super Gravitron is a version of the mobile VVVVVV port, which only contains the Super Gravitron. This PR ports it to the native version. This doesn't do any changes to the options menu however, meaning you can still activate flip mode and stuff, however I don't think it's that big of a deal... (that is to say, I'm tired of working on this PR)

Legal Stuff:

By submitting this pull request, I confirm that...

• [x] My changes may be used in a future commercial release of VVVVVV
• [x] I will be credited in a CONTRIBUTORS file and the "GitHub Friends" section of the credits for all of said releases, but will NOT be compensated for these changes

[AllyTally]

Here's the graphics which would need to be added to the data.zip -- graphics.zip