moved xsl/openbibl.date.xsl functions into main stylesheet

Moved the two templates from xsl/openbibl.date.xsl into the
xsl/openbibl.xsl stylesheet, and rm'ed the date.xsl file. The
two templates were added as xsl:function's.

This moval and deletion were inspired by a baseURI issue in Firefox,
and are a hack around what appears to be either (a) a bug around
xml:base attribute usage in Saxon-CE/GWT/FF, or (b) an unsupported
fix for a baseURI/xml:base action in js/openbibl/saxon.js
added to support synchronous retrieval of resources during
a testing scenario.