Add toString for Graph
Update test
merge
orientation
Merge remote-tracking branch 'refs/remotes/origin/fun_with_validators'
Added node ids (maybe think about different id generation mechanism?)
Added validator for subgraphs search in system graph.
Merge remote-tracking branch 'origin/master'

Conflicts:
	ComputerSystemsSoftwareCore/src/main/java/edu/kpi/pzks/core/model/Graph.java
Merge branch 'refs/heads/master' into aberezovskiy

Conflicts:
	ComputerSystemsSoftwareGui/src/main/java/edu/kpi/pzks/gui/modelview/impl/NodeViewImpl.java