Add datetimepicker to ProblemSetDetail.pm file data fields

Refactor the javascript code into the file Utils/DateTimePickers.
Update jquery-ui-timepicker-addon.js to newest version and revert jquery version to 1.17 instead of 1.18

For some reason jquery 1.18 interferes with timepicker.  This needs to be investigated.
We also need to figure out how to replace America/New_York with EDT and how to
use the locale settings in localOverrides.com

One last puzzle -- we occasionally get "can't recognize zone "  AMerica/New_York.
Where is this misspelling coming from?
Add refactored versions of dateTimePicker scripts.
Fix typo on gradeableProblems (again)
Use only jquery 1.7.1.min.js for now
Created working version of datetime picker

There are still some anomolies with coloring fields that are updated by other fields
Working version for now
Merge branch 'release/2.7' of https://github.com/openwebwork/webwork2 into release/2.7addDateTimePicker
Adding changes from ironparticle for math4 theme
updating math4 theme using ironparticle additions
Correct address of bootstrap.css
Add modifications for math4 theme from ironparticle
Add barrier so that narrow problems don't float up
Replace webwork2_files prefix with a redirect.

The idea is to allow one to server .js files over the 8080 port using a light weight server.
Backoff redirect inside #nav expansion in template -- it isn't working.

Also fix address of jquery.js
Fixed disappearing mathview icon

bootstrap.css was setting img max-width: 100%  which caused the width of this icon to be set to zero.
Probably because the height and width of the surrounding div was set to zero. Consult with css experts
to see if there is a better way to remedy this bug.
Add fix for disappearing mathview icon. Add dateTimePicker fixes.

Merge other fixes from branch 'release/2.7stable' into release/2.7
Add links to jquery-ui-1.8.18.custom
Add missing jquery.js file
Add some checks for defined answer types.

These all seem to have come from checks for answers of type essay.  And they appear when viewing
problems from NAU/discrete math probems.  Perhaps answer type isn't defined there.