Add mod_push_offline module

[MMujtabaRoohani]

This module sends complete stanzas from offline_message_hook to the specified component.

[badlop]

Interesting!

There's just one small warning reported by Dialyzer:

src/mod_pushoffline.erl Line 145: The variable can never match since previous clauses completely covered the type 'undefined'

I guess the most simple solution is to comment that case clause. Can you fix that and push to the PR?

[MMujtabaRoohani]

Thanks for the comment, I have removed the extraneous argument from the add_delay_info function which would also have fixed the error detected by Dialyzer.