Make Ecospace use a mask layer rather than depth = 0

[jeroens]

Changing the depth layer to exclude cells from ecosystem dynamics is a pragmatic way that has been used for years to speed up Ecospace calculations

However, this does not look right, and is prohibitive to building models that include land and water. A new layer is needed where users can sketch which cells are excluded from model dynamics. The cells will not be rendered in the maps

Upon model update and import, this new map will set exclude values where depth values are 0.

The database save logic will remain optimized, not saving any data at depth=0

[joeb]

Disable in the 6.4 release because it has not been fully implemented.

[jeroens]

We have to rethink this. Part of this requirement has become obsolete with issue http://sources.ecopath.org/trac/Ecopath/ticket/1355