Add correct behaviour in case user creates a cycle in the script

[MSattrtand]

Resolves #76

Cycles can only be created when new dependencies are added through the sm:next relation, assuming no files contain cycles. So in scriptService.createDependency I've added a catch that should restore the model before changes were made in case writeScript fails with IllegalStateException, which will be thrown in case we have a cycle in the graph.

Editor will show a message that will indicate that:

[blcham]

I see that it solves some of the issues, but it doesn't make sense to do it this complicated way. Moreover, it has a negative side effect that it modifies the file anyway, forcing the s-pipes editor to reload.

The write method should throw an exception, but it should not empty the file.

I believe there are multiple ways how to solve this issue:

1. the best way:

• we should investigate why we empty file first, this should no happen. If it is happening using:

    public static void writeScript(OutputStream outputStream, Model model) {
        RDFWriter.create()
                .format(new RDFFormat(CustomLangs.SPIPES_TURTLE))
                .source(model)
                .output(outputStream);
    }

you could even reprogram it to:

    public static void writeScript(OutputStream outputStream, Model model) {
        Graph graph = model.getGraph();
        SPipesFormatter formatter = new SPipesFormatter(graph, PrefixMapFactory.create(graph.getPrefixMapping()));
        formatter.writeTo(outputStream);
    }

2. less optimal -- use builder:

    public static SPipesFormatter getScriptFormatter(Model model) {
        Graph graph = model.getGraph();
        return new SPipesFormatter(graph, PrefixMapFactory.create(graph.getPrefixMapping()));
    }

[blcham]

Please try to investigate 1) using test JenaUtils.writeScriptWhenCycleInDependenciesDoesNotWriteToOutputStream()

[blcham]

see my comment