Cmake tex2lyx tests: Take care of initialized userdir

If we are testing tex2lyx the first time, then the userdir
is empty. We call now configure.py to initalize in case it is needed.
The algorithm to detect if reconfigure is needed mimics the lyx behaviour.
Update file formats of test files
Cmake export tests: Use unique file names for exported files

This should prevent possible errors for tests running in parallel.
We now also check for created export file.
  complainer/feature requester: Scott Kostyshak
LaTeXFeatures.cpp: fix bug #9266

mhchem loads amsmath and needs therefore be loaded after it but before packages that redefine commands of amsmath. We already take care of esint but not of wasysym