Added <macro name="substitute-title"> for unsigned articles

Added <macro name="substitute-title"> to cope with unsigned articles and reviews, where the name of the newspaper or periodical (=container-title) needs to stand in place of the author (see CMoS 14.207 and 14.217).
Shorter version of "substitute-title" macro

Now that pandoc-citeproc has been fixed (see https://github.com/jgm/pandoc-citeproc/issues/58), this shorter version of the "substitute-title" macro works in pandoc, too.
added <text macro="title"/> to "substitute-title" macro
Moved <text macro="title"/>
Merge pull request #1028 from nickbart1980/master

<macro name="substitute-title"> for unsigned articles