[ticket/11366] Moving to \phpbb\version_helper

+ bug fix (missing exception)
+ Using \phpbb\version_helper
So, now, the version file have a new format :

	{
		"stable": {
			"<branch>": {
				"current": "<version>",
				[ "announcement": "<announcement link>", ]
				[ "download": "<download link>", ]
			},
			"<branch>": {
				...
			}
		},
		"unstable": {
		}
	}

PHPBB3-11366