* Node validation and error display implemented
* Added option to iterate through nodes in the scene. (Useful to read out data from all the nodes, makes code generation based on the graphs easier.)
* Visual error fix for nodes that change size depending on input, plus minor styling and logic fixes in the example, based on the comments of @russelltg
* Validation extended to handle warnings, based on the idea of @russeltg ; Error display colors now come from the style system; Additional bugfixes
* DefaultStyle.json identation fix
* FlowScene.cpp identation fix
* Travis build test fix