Cluster edge case bugfix + filter flexibility improvements

[hustonm]

Edge case bug fix

• Fixed rare case that produces errors when multiplicity is on but no companions are generated, and added a test for this scenario.

Filter flexibility

• Made get_obs_str function more generic, which should make it easier for a user to use any additional filters available in synphot. Also removes a step when adding new filters if the standard string formatting is maintained, but a user can add more special cases as needed.
• Added some new filter systems: Hipparcos, Kepler, OGLE, TESS, Tycho, Washington, Subaru HSC.
• Updated DECam filters to latest available

Also addressed a couple super simple numpy deprecation warnings.

I'll probably have more filters at some point, but I'm not sure when, so I figured I'd make this PR now for whenever the next review of PRs happens.