add login route

app/templates/common/topnav.html

@@ -18,6 +18,7 @@
     <input type="hidden" name="return_to" value="{{request.path}}">
     <input type="text" placeholder="Username" name="username" autocomplete="username" required>
     <input type="password" placeholder="Password" name="password" autocomplete="current-password" required>
+    <span><input type="checkbox" name="remember" id="remember"> <label for="remember">Remember me</label></span>
     <input type="submit" value="Log in">
     <a href="{{url_for('users.sign_up')}}" class="linkbutton alt">Sign up</a>
   </form>