Do not link favorites to users; make them global

After a design discussion, we decided that favorites should not be
linked to users, but should be global; anyone with the right to
create questions should have access to the list of favorites.
In-progress: rename favorite to question template

This is commit 1 of 2; this one renames files, the next commit will
modify files to rename classes and functions.
In-progress: rename favorite to question template

This is commit 2 of 2, renaming classes and functions.
Allow creating questions from templates

The "Make Question into Template" and "Save as Template" buttons
aren't implemented yet, so users can't actually create new templates.
But if there are templates in the database (such as the ones I added
by hand to test this functionality), they can now be selected for new
questions. The next commit will allow saving new templates, at which
point the templates feature will be fully implemented.