feature: show all free rooms at once

[richard-xue-vrx]

Right now, for finding rooms on Freerooms requires going to individual buildings to find and see what rooms are free at any given time.

We want a feature that allows any user to easily see ALL rooms that are free on campus at any given time. This will require some sort of design in the frontend, as well as searching through all rooms to see what rooms are free and unoccupied.