Remove Loading text from the loading screen in production build

[keiffer01]

Issue summary

Authenticating the current user is not instantaneous, and so for a split second the user is able to see the page load before Firebase realizes that they are not currently signed in and kicks them back to the landing page. This may be a problem if the user is able to, even temporarily, see the details of a trip itinerary. A fix for this could be a simple loading screen that hides page contents, which is only removed after the user has been authenticated.

Expected behavior

Page details are completely hidden from the user until they have been authenticated.

Actual behavior

Page continues to load even while the user is still being authenticated.

[keiffer01]

UPDATE: Using React, the page is simply not loaded until the user is fully authenticated. The browser temporarily shows a blank screen that says "Loading..." while this happens. This is left in for testing purposes, in the deployed build the loading screen should be made blank (since the authentication happens relatively quickly, the split second blank screen should be fine).

The title of this issue has been renamed from "Add simple loading screen to all pages (except the landing page)" to "Remove Loading text from the loading screen in production build".