Update FlashPlatform.hx to allow template feature as the other platforms

We had the need to use the templace system of openfl tools on *flash* platform but was deactivated.

We think it is better to let the user have control over it, but give more power to the tooling.

(eg, here we wanted to copy the airApplication.xml configuration file as a template  for AIR projects, but might be lot of different things).

Thomas