add BASS and MzLS filters used by the Legacy Surveys

[moustakas]

Adding the grz filters used by the northern DESI Legacy Imaging Surveys--
https://www.legacysurvey.org/
https://speclite.readthedocs.io/en/latest/filters.html#desi-imaging-survey-filters

Note that data/filters had been added to the .gitignore file, so I had to remove it to add more filters. Let me know if you'd like it restored to its original form.

[bd-j]

Thanks @moustakas! I had data/filters/ in .gitignore' (and would use git add -f`) just for my own convenience as I kept a bunch of prep code or atypical filters in the same place, but this is probably best practice and I can move that code elsewhere.

For future reference the filter naming convention has been to use underscores, but I think the dashes here are fine.