Display "wait/processing" pages
Display "wait/processing" pages while background process is in progress, especially needed for pre-/post-processing of larger datasets.
- Generate "wait" page, save it on disk and send it to browser
- Update "wait" page on disk in the background, and refresh "wait" page in the browser: auto-refresh and refresh button with cmd=read
- When background process has finished, replace "wait" page on disk with disables auto-refresh and refresh button with cmd=update