Add support to ignore trash for certain mounts

Add support for x-gvfs-notrash mount option, which allows to disable trash functionality for certain mounts. This might be especially useful e.g. to prevent trash folder creation on enterprise shares, which are also accessed from Windows...

See also corresponding gvfs merge request: gvfs!89 (merged)

See corresponding bug reports:

• https://bugzilla.gnome.org/show_bug.cgi?id=729385
• https://bugzilla.redhat.com/show_bug.cgi?id=1096200