Fix missing Front Controller

Added `app_dev.php` front controller to the demo url.
bug #3871 Fix missing Front Controller (parthasarathigk)

This PR was submitted for the 2.4 branch but it was merged into the 2.3 branch instead (closes #3871).

Discussion
----------

Fix missing Front Controller

Added `app_dev.php` front controller to the demo url.

Commits
-------

f2df407 Fix missing Front Controller