Interface to PGMiner is is not sufficiently robust

[Danil Sokolov]

PGMiner interface needs cleaning and some improvement.

1) If Process minimg -> Extract concurrency of selected graphs is applied to a CPOG without scenarios the exception is thrown at the late stage of parsing PGMiner output. Instead a user-friendly warning should be issued before proceeding to PGMiner.

2) The code of PGMinerSelectedGraphsExtractionTool needs cleaning (unused variables, unnecessary complex code)

Note that the following code can be replaced by "graph.trim();"
    while (graph.startsWith(" ")) {
        graph = graph.substring(1);
    }
    while (graph.endsWith(" ")) {
        graph = graph.substring(0, graph.length() - 1);
    }

Probably the same applies to PGMinerImportTool.