Fix unusual navbar link behavior in Firefox

In Firefox, nav links can get stuck in :focused state by
click-dragging on them, or clicking them then navigating 'Back'.

Previously, this would show the button as grey (on a grey bkg).
Now, it shows as the 'hover' color (orange).

Fixes #157
Fix student_waitlist_rsvps to be more likely to work in postgres
Changes to event time display on homepage

Upcoming events show times for each session as '[date] from [time-time]'
Old events just show the date of the last session