Add letter_opener_web

to present emails in the browser in development mode.
Using letter_opener in combination with Vagrant does not work
because it's not possible to launch a web browser in your
Vagrant box. Fixes #817.

config/routes.rb

@@ -10,6 +10,11 @@ Osem::Application.routes.draw do
                path: 'accounts'
   end
 
+  # Use letter_opener_web to open mails in browser (e.g. necessary for Vagrant)
+  if Rails.env.development?
+    mount LetterOpenerWeb::Engine, at: "/letter_opener"
+  end
+
   resources :users, except: [:new, :index, :create, :destroy]
 
   namespace :admin do