Remove env-section from apns.app.src

The env-section effectively overrides any value set using
application:set_env/3 before apns is loaded making it harder to test,
etc. The data in env doesn't really add anyhing since the user most
definitely want to update that with it's own info

A default app.config is added to priv/app.config
Merge pull request #32 from bipthelin/master

Remove env-section from apns.app.src