Rework configuration process

Dynamically loads `config.json` on startup.

Fixes #167, #284, #449, #486

Change-Id: I9efb1079c0c88e6e0272c5fda734a367aa8f84a3

src/synapse/authProvider.js

@@ -3,9 +3,6 @@ import { fetchUtils } from "react-admin";
 const authProvider = {
   // called when the user attempts to log in
   login: async ({ base_url, username, password, loginToken }) => {
-    // force homeserver for protection in case the form is manipulated
-    base_url = process.env.REACT_APP_SERVER || base_url;
-
     console.log("login ");
     const options = {
       method: "POST",