Summary
A new module enet has been added to the ESP-r suite which supports
the graphic definition of air flow networks, including the attribution
of nodes, components and connections. This approach provides
additional feedback and clarifies the relationship between nodes and
components. ESP-r modules now accept both current and graphic
network files. New networks can be composed via existing menu-driven
facilities or the graphic facilities.

Example models with both text and graphic network definitions have
been included. The databases folder now includes an icons file with
templates for flow nodes and a range of generic and bespoke
components which enet draws from.

During testing height difference errors were found in some
existing training models with flow networks and were corrected.
Otherwise, users working with existing models will not notice
differences.

This is an initial pass through the code, following interactive
tests final debug statements will be commented out (in a subsequent
commit).

Testing:
- A number of existing flow networks were re-created via the graphic
  facilities and assessments carried out. For equivalent models the
  differences were at the third decimal place.
- A full syntax check has been carried out.
- Tester.pl was run against a May 2014 svn version with most
  models passing. Intent is to re-run against the git master
  to double check differences in more detail.