Merge branch 'release/2.8' of https://github.com/openwebwork/webwork2 into release/2.8
Make minimal tweaks needed to make LibraryBrowser3 list problems from sets and from Libraries
Merge branch 'release/2.8' of https://github.com/openwebwork/webwork2 into release/2.8_librarybrowser3tweaks
Correct behavior of HINTS and SOLUTIONs

Solutions are shown immediately to students in HTML mode after the due dates
Hints are shown to students in hardcopy after the answer date if they request it
Solutions and hints are not shown to instructors in hardcopy mode unless they request it.
Clarify comment
Merge pull request #228 from mgage/release/2.8_hint_solution_tweaks

Release/2.8 hint solution tweaks

This goes with the corresponding pull request for pg.