This change swaps out the top-level application to render via react

instead of an underscore template. The existing routing code has been

moved into a new component called <LegacyRoutes>, which is responsible

for managing all the child backbone views that the ApplicationView

used to handle. As pages are redone to be react components, those will

move into their own <Route>s, and eventually the legacy routes will

disappear.
This also switches the main layout to CSS grid, which works way better

than the old hacky piling-on of backbone grid classes did.
Finally, there were a couple bugs in the data and display of the

"All Users" page that were getting swallowed by the previous method

of attaching views but were causing exceptions now. Those have been

fixed.

Went through all pages and saw that everything still loaded properly.