Future-proof automation track GUI 'extra' XML (<GUI><AutomationChild automation-id="gain"> instead of <GUI><gain> so Parameter.to_string isn't used as an XML node name).
Fix automation track controller bar shown/hidden state.
Fix automation track initial show bug.
git-svn-id: svn://localhost/ardour2/trunk@2103 d708f5d6-7413-0410-9779-e7cbd77b26cf