[read] make visualize_edges more friendly for overlay by default

gridlock/read.py

@@ -182,7 +182,7 @@ class GridReadMixin(GridPosMixin):
             plane = Plane(**plane)
 
         if pcolormesh_args is None:
-            pcolormesh_args = {}
+            pcolormesh_args = dict(alpha=0.8, colors='gray')
 
         grid_slice = self.get_slice(
             cell_data = cell_data,
@@ -212,6 +212,9 @@ class GridReadMixin(GridPosMixin):
 
         mappable = ax.contour(xcmesh, ycmesh, grid_slice, levels=levels, **contour_args)
 
+        if finalize:
+            pyplot.show()
+
         return fig, ax