WIP: Single-line format for reservations
LTSINSCRIP-76 , LTSINSCRIP-75 (sort of) and more RailsUJS stuff

This branch consists of a marginally cleaner and more performant rewrite of the
functionality on the "Reports" admin page.  I've located it at Reservation#index, because
there's no user listing of reservations, and it seemed to fit.

Additionally, delete and update functionality for reservations is handled
via ajax (Rails UJS, to be specific).  I'm doing it in the low-pass way, by letting
the Rails UJS helper eval returned JS.  We have CSRF protection enabled, so it's not
insecure, but arguably it could be done more cleanly by hanging off the 'ajax:success'
and 'ajax:failure' methods.  Not gonna, for now.
Fixes for problems introduced in b065e2cf37a8ea11d711669129e9e68cbe0b66bf, mostly discussed in  CR-LTSINSCRIP-8

The noted exception - the new users/reservations action is needed because previously the index view was used for users and admins.
Fix to sidestep broken ActiveRecord method in historical migration