Error reforms

Hi,

I've moved all the Freemarker templates associated with errors and exceptions to the one directory.

I've also added exception handlers for amber InvalidObjectIDException and amber NoSuchObjectException.  Invalid object IDs have a template that explains (briefly) what went wrong, and NoSuchObjectExceptions do the same as Banjo's RecordNotFoundExceptions.

We also needed to log error messages to `stdout` properly.

Huw