2811: Add low-level support for XSLT

Expand xmlParse.xmlfile2dict to take an xslt_file argument.
Uses libxml2 and libxslt to do the XSL transform.
2811: Add support for directory of XSLT files
2811: Support for XSLT path in Params class
2811: Add -xslt_path option to reconfig_frontend