Frame and Band interchangability

[manthey]

Tile sources have the concept of bands (channels) and frames (multiple images). Some UIs only handle one or the other. Rather than have clients handle both, perhaps support a bandAsFrames option to tile sources that would, for make bands appear as frames. This could have some sort of threshold (only if more than 3 or 4 bands). The converse could also be done (framesAsBands).

This may not actually be useful enough to be worth the complexity.

[manthey]

This should probably just be subsumed into the functionality in #680.