Replace iCal::Parser with Data::ICal

[bigpresh]

iCal::Parser doesn't let us easily see details of recurring events; it would be nice to add recurring events to the destination GCal properly.

Data::ICal will let us do so - and, in fact, setting recurrence info in Net::Google::Calender::Entry events requires a Data::ICal::Entry::Event object anyway.

Shouldn't be too difficult to convert, and the new-found tests should ensure it works \o/