Polling improvements

Several views poll Web Services, e.g., the Processes view polls to check for updates to the "Downloads" tab.

The following improvements have been made:

• Processes view
• If this is not the active view then polling for the Background and Scheduled grids takes place every 15 seconds rather than every 5 seconds
• Polling for the Downloads grid takes place every 15 seconds rather than every 10 seconds
• NOTE: If an incomplete Download is detected then polling takes place more frequently to check the updated status of the Download
• If the User has been signed out (e.g., due to inactivity) then this is detected and multiple requests to retrieve information are no longer sent until signed in again

These changes have been made to prevent unnecessary requests being made to the Web Server and from the developer console in a web browser (usually shown by pressing F12) showing that many 401 (unauthorised) errors are occurring when the User's session has timed out.