Adding the iCal export to the calendar action

So, I've done it (see the [original comment that started this stuff](http://xataface.com/wiki/Calendar_Action#comment-1417763323)), I add the ability to export table as iCal files. This is visible when in the calendar tab of the calendar action, as a action icon (icon in public domain, taken [here](http://commons.wikimedia.org/wiki/File:New_Year_Calendar.svg?uselang=fr).
I use the [iCalCreator lib](http://kigkonsult.se/iCalcreator/index.php) from [KigKonsult](http://kigkonsult.se) which is LGPL'ed.
xCal format may be easily supported as iCalCreator seems to support it already, but I did not make it as I don't care.