Allow searching for multiple wavebands in registry.regsearch()

[cbanek]

In #175 we fixed a bug with searching for wavebands, and @msdemlei had the idea of being able to search for multiple wavebands too, which sounds like a good one. Just noting that as a separate feature so we can close out the bug and keep track of this in the future.

[msdemlei]

With #289, you can create a Waveband constraint with multiple arguments, which will do what's proposed here.