set_lake_z overhaul

[kbevers]

Handle db-stuff with GDAL in set_lake_z needs (instead of psyopg2)

set_lake_z uses psyopg2 as a database handler. This is nice when you have access to a postgres database, but otherwise sucks. With GDAL as a the database front you are also able to use other datasources, such as shape-files or spatialite-databases.

Database setup

The current interface for setting up the ekstra columns in the lake table is very clumsy. Use "db" as las-input, then use "-db_action setup". After that a new similar call has to be made, this time with "-db_action reset" to initialize the new columns with data.

Documentation

The help text for set_lake_z specifically says that you can use the path to a shape-file as the db_connection. This is not possible with the way the script is set up at the moment.