[ENH] calendars: Add simple "export as ical" button to calendar events - uses existing code in tiki-calendar_export_ical (thanks marclaporte)

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/11.x@46949 b456876b-0849-0410-b77d-98878d47e9d5
[FIX] Use Twitter API v1.1 as v1 is not available any more


git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/11.x@46950 b456876b-0849-0410-b77d-98878d47e9d5
[ENH] calendars: Perm check for first "export as ical" button (assumed to be y in edit mode)

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/11.x@46951 b456876b-0849-0410-b77d-98878d47e9d5