Updates for compatiblity with Joomla 3.9
Fix to exclusive locking during AJAX calls.
Uses AJAX to display list of campaigns as they are retrieved from Constant Contact API.
Previously, Constant Contact accounts with many campaigns would take a very, very long time to load and could have a gateway timeout. Now we load campaigns with AJAX and display them as they show up, avoiding this problem. (Cached campaigns are still displayed immediately).
Now correctly handles Constant Contact accounts with more than 50 campaigns.
Uses CtCt API data pagination to retrieve entire contents of account. API doesn't return items in chronological order, they appear to be random, so we need to retrieve entire account even if we only want to display the most recent few.