HPCC-9468 Main Graph Depth

Restrict initial load to 2 levels deep.
Allow overriding default DOT attributes (good for turning off splines).
Added Zoom and Find Icons.

Fixes HPCC-9468

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #4531 from GordonSmith/HPCC-9468-Main_Graph_Depth

HPCC-9468 Main Graph Depth

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>