SitesController now has fleshed-out methods and views
for #index, #create, #show, and #update. This provides functionality allowing
the listing and creation of sites, as well as allowing the addition of
interlockings to existing sites. Next to do is to allow the editing and
deletion of interlockings (though the latter is somewhat more involved as it
will necesitate ditching all the configured static data and accumulated
events and statistics!)