Add new Tramp connection method "owncloud"

Add new Tramp connection method "owncloud"

* doc/misc/tramp.texi (all): Use @acronym{GNOME} thoroughly.
(Using GNOME Online Accounts based methods): Rename from
"Using Google Drive".  Add `owncloud'.
(GVFS based methods): Add `owncloud'.

* etc/NEWS: Add Tramp connection method "owncloud".

* lisp/net/tramp-gvfs.el (tramp-gvfs-methods): Add "owncloud".
Remove goa methods if not supported.
(tramp-goa-methods, tramp-goa-service, tramp-goa-path)
(tramp-goa-path-accounts, tramp-goa-interface-documents)
(tramp-goa-interface-printers, tramp-goa-interface-files)
(tramp-goa-interface-contacts, tramp-goa-interface-calendar)
(tramp-goa-interface-oauth2based)
(tramp-goa-interface-account, tramp-goa-identity-regexp)
(tramp-goa-interface-mail, tramp-goa-interface-chat)
(tramp-goa-interface-photos, tramp-goa-path-manager)
(tramp-goa-interface-documents)
(tramp-gvfs-owncloud-default-prefix)
(tramp-gvfs-owncloud-default-prefix-regexp): New defconst.
(tramp-goa-name): New defstruct.
(tramp-gvfs-stringify-dbus-message): Handle all consp messages.
(tramp-dbus-function, tramp-gvfs-get-remote-prefix)
(tramp-get-goa-accounts): New defun.
(with-tramp-dbus-call-method): Use it.
(with-tramp-dbus-get-all-properties): New defmacro.
(tramp-gvfs-url-file-name)
(tramp-gvfs-handler-mounted-unmounted)
(tramp-gvfs-connection-mounted-p, tramp-gvfs-mount-spec):
Map between "owncloud" and "davs".
(tramp-gvfs-maybe-open-connection): Set "vector" connection property.

* test/lisp/net/tramp-tests.el (tramp-gvfs-handler-askquestion):
Suppress run in tests.
(tramp--test-owncloud-p): New defun.
(tramp-test11-copy-file, tramp-test12-rename-file): Use it.