Initial version of the duplex scanning of simplex surveys (fixes #1)

This is an initial version that only got basic testing, more testing
needs to be done.
If blank pages are included in the scan then the recognition process
will be *very* slow right now because the matrix recognition is very
inefficient when it does not give up.
Image class needs to be importat for the upgrade.
Don't search for lines as aggressively.

The corner search algorithm is rather bad, and if there is nothing
to find it would slow down a *lot*. The change here is to not search
quite as agressively.