Ignore testfiles directory
Remove trendminer prefix from imports (not necessary)
Check whether or not XML files in uploaded archive are well-formed
Introduce basic XML schema and check files against it before processing them
Fix validator for xml well-formedness: Don't try to access extracted
files by their sanitized names. We don't alter their names when
extracting them, so xmlwf won't find them if we pass sanitized
versions of their names.