for xml files (xtc, cpf), we should use authorized style sheet

[jwaldmann]

current situation:

• some benchmarks have wrong location of xtcHTML.xsl
• some proofs have no reference to cpfHTML.xsl

result:

• rendering does not work, so effectively no-one can view these data easily (could use show-source in the browser but that's clumsy)

this should be repaired by

• not trusting what provers write there
• insert appropriate xsl reference