add ability for custom branding images

app/views/shared/_header.html.erb

@@ -1,14 +1,9 @@
 <div class="header py-4">
 	<div class="container">
 		<div class="d-flex">
-			<% if current_user %>
-				<%= link_to current_user.main_room, class: "header-brand" do %>
-					<%= image_tag("logo_with_text.png", class: "header-brand-img") %>
-				<% end %>
-			<% else %>
-				<%= link_to root_path, class: "header-brand" do %>
-					<%= image_tag("logo_with_text.png", class: "header-brand-img") %>
-				<% end %>
+			<%= link_to (current_user ? current_user.main_room : root_path), class: "header-brand" do %>
+				<%= image_tag(Rails.configuration.branding_image.blank? ? "logo_with_text.png" : Rails.configuration.branding_image,
+					class: "header-brand-img") %>
 			<% end %>
 
 			<div class="d-flex ml-auto">

config/application.rb

@@ -50,5 +50,8 @@ module Greenlight
 
     # Configure custom banner message.
     config.banner_message = ENV['BANNER_MESSAGE']
+
+    # Configure custom branding image.
+    config.branding_image = ENV['BRANDING_IMAGE']
   end
 end

sample.env

@@ -53,3 +53,7 @@ ALLOW_GREENLIGHT_ACCOUNTS=true
 #   The recommended prefix is "/b".
 #
 RELATIVE_URL_ROOT=/b
+
+# A URL to the image you want to appear in the top right corner of Greenlight.
+# By default, this is the BigBlueButton logo.
+BRANDING_IMAGE=