fix views according to newest qwat model

[tudorbarascu]

Hi,
The pull is mainly for review (not finished yet) as there are some things that I would like your opinion on.

These are the errors that still exist.

psql:qwat_to_epanet_views.sql:22: ERROR: relation "distribution.od_reservoir" does not exist
LINE 3: from distribution.OD_RESERVOIR;
^
psql:qwat_to_epanet_views.sql:74: ERROR: missing FROM-clause entry for table "p"
LINE 2: select v.id, p.fk_pipe_in as start_node, p.fk_pipe_out as en...
^
psql:qwat_to_epanet_views.sql:85: ERROR: column e.id does not exist
LINE 5: on e.id = n.id;

Thoughts regarding the valve view:

• A valve shouldn't have an underlying node in qwat as it shouldn't split the pipe
  Basically, valves shouldn't exists at pipe ends in GIS. I believe having a pipe vertex where the valve touches the pipe is a good solution.
• The current valve table in qwat link had a fk_node to the underlying node (probably will be erased in future models) and also a fk_pipe (usable for us)

Do you think that we should use the underlying pipe start and end nodes and use it for the valve direction?
I am thinking of using the underlying pipe vertex and split the pipe in the view if the valve is closed etc.

Thoughts?