Repair menu highlighting, both for main menu and submenus

During the recent improvements made on the website, the menus and
submenu highlighting for selected menus fell into disarray.
Correction requires changes to the CSS and templates both, because
Django doesn't really have a convenient way to set variables in
templates to use to solve this.

There are still a few submenu items highlighting not working even
after this commit. More work needs to be done.

Rename Members->Projects in menu navigation et al

Due to confusion about "members" and "supporters", we want at least the
menu navigation to not use the phrase "members" since some Supporters
expect that to refer to a type of donor.

While we will not be rebranding "member projects" fully at this time, we
want to favor the term projects.

A few additional changes, in particular moving files from members/ ->
projects/ directory will be needed in next commit.