Replace "phpBB Group" with "phpBB Limited"

- In the previous PR, some words had forgotten to be replaced.
Update footer in qi_functions.php

- add https
- add 3.1 reférence
- be compliant with qi_main.php and overall_footer.html
Merge pull request #39 from phpbb-fr-com/master-pr_39

Forgot to update footer and some "phpBB Group" in in a previous PR