COMP: Increase DOT_GRAPH_MAX_NODES.

For

warning: Included by graph for 'itkObjectFactory.h' not generated, too many
nodes. Consider increasing DOT_GRAPH_MAX_NODES.

and similar warnings.

Change-Id: I456d624513e3a10243447b3162b3b06ede65cef3
Merge topic 'doxygen-warnings'

8eddcf69 COMP: Increase DOT_GRAPH_MAX_NODES.