Nelson Ben authored Jan 30, 2022 and Germán Poo-Caamaño committed Feb 23, 2022

Issue #1333 removed Evince ability to run any command
from pdf 'launch action', while the security concerns
brought up in #1333 were valid, the measure implemented
was maybe too drastic, as there are valid use cases
where launching a pdf is needed.

For instance, the cases described in issue #48, one of
them is the document 'Nissan Patrol Maintenance Manual'
which is comprised of several pdf files, where there is
one acting as index for the others, this index pdf file
uses the launch action to open the other pdf's.

So this commit allows to launch a file from a link
action only when:

- that file is a pdf file.
- the launch action originates from click event,
  to be sure the user requested the action.

Besides, we don't just let the system execute the
file, but because it's a pdf we do it ourselves by
launching a new evince instance (or if that file was
already opened then presenting its window).

Fixes issue #48