erp5_document_scanner: Extend code to disable button properly and display a preview before open Cropper

erp5_document_scanner: move the caman code into a separate function, where the promise canceller will cleanup the memory

erp5_document_scanner: Fix css to delete button and make thumbnail and new page button with same size

And add comments

erp5_document_scanner: add an alarm which will delete outdated (>5 days old) active_process created by the dialog.

With this, we can search easily active processes used by document scanner and remove them

With the size close to the thumbnail, to replace the `new` button text

Drop the current displayed text