When WOPI's CheckFileInfo or GetFile responds with status code other
than HTTP 200, show a message to the user indicating some problem in the
storage.

Currently, we open an empty document if storage doesn't return a
document which surely is not correct.

Mention the storage server address when asking user to contact the
server administrator to be more friendly.

Combination of following cherry-picks from master:
(cherry picked from commit 2e9e6a75)
(cherry picked from commit bcf958c5)
(cherry picked from commit aed840ea)
(cherry picked from commit 1ea87b62)

Change-Id: I7e2455d3c4da8be2c476460b94812174c34fe529
Reviewed-on: https://gerrit.libreoffice.org/37903


Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>