mate-document-viewer 1.6.1 nows builds and supports XPS.

Hi,

Here are some fixes for `mate-desktop-viewer`.

  * Removed impress support because it has been removed upstream.
  * Migrated to `libsecret` as upstream.
  * DVI (`texlive-bin`) is now really optional.
  * Added XPS support.
  * Fixed a linker error, altough I'm still discussing the root cause with stefano-k and infirit.

Regards, Martin.