Add Test for Admonition XREFS
Add Test for Admonition XREFS

This commit adds 3 new scenarios, each with 3 sub scenarios to test
the new xrefs to admonitions. The 3 scenarios are as follows:

* Testing whether xrefs to admonitions with titles generate with the
correct text
* Testing whether xrefs to admonitions without titles generate with ???
* Testign whether xrefs to admonitions generate with the pagenum class
given the additions to the xref.elements.pagenum.in.class param

oreillymedia/HTMLBook,oreillymedia/HTMLBook,oreillymedia/HTMLBook