-Stylistic changes to the footer
-Changed name of cl-notebook SSE channel (now :cl-notebook-updates)
-Cell-controls, main-controls and footer are now properly z-indexed
-the result-values template now checks whether there are any (some forms can return `no-value`, rather than an actual value)
-Removed unused callback from notebook/current
-Going to / now shows the "first" notebook rather than a blank page
-Split initialization and built-time functions off into their own file
-When trying to view a nonexistent book, a notice to that effect is now displayed
-Added TODO note