Choosing the algorithm state

We have two algorithm states:

• UllmannState
• VF2State

Pass sourceGraph and targetGraph through constructors.

Also if you have ability to extend the State to implement another subgraph isomorphism alogrithm, welcome make a pull request!

...
for (Graph targetGraph : targetGraphs) {
    for (Graph sourceGraph : sourceGraphs) {
       // choosing an algorithm state
       State state = new UllmannState(sourceGraph, targetGraph);

       // the following code ...
   }
}
...