[Load Digraph/Design] preserve/remove subgraph keyword?

[harshsikhwal]

Possibly preserve subgraph keyword. If not present, should not add to file.

For example:

Input: b -- { c e };

The dot read should not have "subgraph" like:

	b -- subgraph
	{
		c;
		e;
	}

Note: All the graphs generated from csdot should have that keyword.