update creating a new unit to use an empty template. Also twiddle the units.html and base.js where we put the unit Location on the <li> element

Hook up the component delete button to the backend. Don't break if the process of updating a parent unit after deleting is interrupted (leaving a pointer to a missing module)

add subsection edit page to the project with a shared 'unit' widget that will render out unit lists. Both edit_subsection and overview.html will share this widget

add subsection edit page to the project with a shared 'unit' widget that will render out unit lists. Both edit_subsection and overview.html will share this widget