This patch removes the options to link images from the gallery.
Users should never link to the gallery. The links wouldn't work anymore if you just change the operating system, because the gallery is on a different place.

Changes:
* Removed option in "Bullets and Numbering" dialog to link graphical bullets
* Change the Gallery image context menu.
Before:
  Insert
    Copy
    Link
    Background
      Page
      Paragraph
  ...

Now:
  Insert
  Insert as Background
    Page
    Paragraph
  ...

Change-Id: I699042a7d7a27369775f9ee4c14c4a6964489a92
Reviewed-on: https://gerrit.libreoffice.org/5141Reviewed-by: Luboš Luňák <l.lunak@suse.cz>
Tested-by: Luboš Luňák <l.lunak@suse.cz>