Redirect to previous page after login

Closes #24

vedia.rb

@@ -134,7 +134,11 @@ post '/login' do
     session.clear
     session[:user_id] = user.id
     session[:timezone] = params[:timezone]
-    redirect '/'
+    if params[:r]
+      redirect params[:r]
+    else
+      redirect '/'
+    end
   else
     @error = _("Incorrect email or password.")
     erb :login
@@ -598,10 +602,11 @@ helpers do
   end
 
   def require_login
-    redirect '/login' unless current_user
+    redirect "/login?r=#{request.path}" unless current_user
   end
 
   def require_admin
+    require_login
     redirect '/' unless is_admin
   end