Comment 2 for bug 1981774

Working branch user/jeffdavis/rt92002-lp1981774-bootstrap-buttons has a fix:

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/jeffdavis/lp1981774-bootstrap-buttons

There are two commits. The first commit cleans up all uses of the opac-button class in the Bootstrap OPAC. The second commit fixes a typo involving a button class in the curbside pickup UI.

I didn't do anything about the results_header_btns class because I couldn't get the relevant button to display (perhaps this is dead code?). I also didn't do anything about the classes that lack CSS rules in Evergreen.