move postAjax function into a new file
big rework of error handling on requests
- central point for checking for 'error: "out of date"' response from server
- in 'out of date' state, an error dialog is shown and no further requests are sent to the server
- request queue has central point for request adding - now request count is accurate, not just for COMM requests
- request error count is cleared after a period of no requests failing