database: Make loading of models cancellable
Add date utility struct
job-order-list-view: Cancel loading before starting a new one

If the view is currently loading, cancel it first before starting a new
loading.
job-order-list-view: Don't reload after closing editor in search mode

When the editor is closed and the view is currently in search mode, don't
reload to allow the user to view again the search results.
job-order-list-view: Add search for job order start date

When in search mode and the search text changes, try to guess if the search
text is a date or a date span. If successful, create a filter for the date
or date span then reload the view.