[ticket/11366] Extension's version's check

Add a feature to check automatically the version of the installed
extensions. The informations are cached for 24 hours (like for the
global update check on the main page of the acp).

The informations about the versions are display both on the global list
and on the detailled page.

To do this the developper has to add some informations into the composer.json :

    "extra": {
		"version-check": {
			"host": "<the host>",
			"directory": "/<the directory containing the file>",
			"filename": "<the composer.json of the latest version>"
		}
    }

and to let a version file available. The version file should look like phpbb's: http://version.phpbb.com/phpbb/versions.json

A notice is displayed when the "extra.version-check"
informations are missing.

Ticket: https://tracker.phpbb.com/browse/PHPBB3-11366

PHPBB3-11366