Add GBC exclusive tests

[pinobatch]

Now that the GB suite's help screen is enhanced for Game Boy Color, we can decide which tests exclusive to GBC can be added to the list for the benefit of Game Boy Player owners.

• PLUGE
• Gradient color bars
• SMPTE color bars
• Color bars on gray
• Color bleed

If this were Super Game Boy, I'd suggest SGB audio and chroma crosstalk. But after adding GBC tests and GBC enhancements to existing tests, I'm not entirely sure I'll be able to fit SGB tests in the remaining space on the 32 KiB Catskull cart that we're currently targeting.

I'll request GBC enhancements to existing tests in a separate issue.

[pinobatch]

I have 1726 bytes left after having fixed #2.

[pinobatch]

Because I have about 600 bytes left after adding draft help text for these tests, I'll have to put this one on hold until I can figure out compression for the rest of the suite. But once that happens, I've made rough PNG mockups of the GBC-exclusive tests.

[pinobatch]

I was able to compress all tilemaps (stopwatch, linearity, sharpness, and the mono and color portraits in shadow sprite) and unify the tilesets used by Lame boy, Motion blur, and Overscan. This bought a bit of space to make SMPTE color bars, Color bars on gray, and Color bleed, with 740 bytes left. I'm not certain whether that'll be enough for PLUGE and Gradient color bars.