[FIX] countdown: Handle text param as described, i.e. if empty then use the defaults.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@49078 b456876b-0849-0410-b77d-98878d47e9d5
[ENH]Add {{domain}} as a new wiki argument variable. Thanks Tom Jarvis and Jonny for tips and comments on the devel list.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@49079 b456876b-0849-0410-b77d-98878d47e9d5