Modularised the strike-out function

In preparation to catch exceptions
Return 200 if good or 500 if error

Implemented the function, two-oh-oh, that will return the correct
response if all goes well. While the function five-oh-oh will return the
error code.
Save the PDF form when an exception occurs

The PDF form should be saved under /var/tmp/strike2-debug... directory.
Merge pull request #5 from ministryofjustice/proper-status

Workarounds for exceptions