Add a 'new journal here' button

The journal tiddler will be tagged with the name of the current
tiddler. This is similar to how the new here button works.

(Would have liked to reuse the journalButton code which is almost
identical between new-journal-here and new-journal, but I'm not
sure how to do it.)
Merge pull request #959 from simonbaird/new-journal-here

Add a 'new journal here' button