Periodic tasks are special in that they are usually kept around and
started based on a schedule. A new component checks periodic tasks and
submits them in the queue once they are due.
In order to avoid duplicate periodic jobs, the tracker of a job is
used to store the periodic job id. Each time a periodic task is due,
it is first checked if there is a job running (or queued) for this
task.
The restriction that only pdf files can be uploaded is removed. All
files can now be uploaded. The processing may not process all. It is
still possible to restrict file uploads by types via a configuration.
The viewerJS library can display PDF files easily using pdfjs. Another
attachment route redirects to the viewerjs application to display the
current attachment.
The attachment responses have been improved in that now the response
headers are added to all responses. Additional a HEAD route has been
added to support the viewerJS application.
