CONTENTdm: Convert to lxml, fix simple project client

refs #7239

Update simple project client code to not read from server, just parse METS
file. Use element names as column headers and element text values for the
row values.  Use both DC and non-DC metadata.

Minimally convert from using xml.dom.minidom to the more powerful
lxml.etree. Update code using minidom, cleaning up and adding docstrings as
well.