WebSubmit: do not support PDF/A with GS version < 8.65
- Versions of GhostScript prior to 8.65 are buggy or not supporting at all PDF/A creation (such as on SLC5). PDF/A creation is disabled if the minimal version requirement is not met. (closes #345)
- Fall back on PDF creation using ps2pdf when converting from PS and PDF/A support is not available.
- More verbose messages when checking for OCR, PDFOPT, PDF/A support.