Another attempt at a sidemenu

I had to send another pull request for sidemenu; this pull request is a continuation of #502.  In attempting to update the pull request by pushing to my remote branch, I broke some things and made it impossible for me to figure out how to fix things.  So I started from a fresh branch.

Only the files math4-overrides* were changed significantly; and math4.js, in which I had to comment out the block related to the current site navigation behavior within math4.js to prevent any conflicts with the new site-navigation behavior in math4-overrides.js.  I also made the sidemenu responsive at 825px.

I also found out the reason why I had so many modified files showing up as modified/untracked before.  I used chmod -R 777 . on the guest OS so that I could edit files on my host machine without permissions errors.  I found that I should instead use chown -R wwadmin:wwadmin .