Open PR to jgrapht for interval graphs

[pdelvo]

[PhoenixIra]

To gather up things, that have to be done:

• review and merging the last tests
• refactoring the method isIntervalgraph(graph) (computeIntervalgraph or something like this)
• creating an empty list for the interval list, if the graph is empty

[christophgruene]

Everything should be done now... @pdelvo, you may merge the PR from @Watercrystal into your PR

[PhoenixIra]

To again gather up things, that have to be done (feel free to mark todos if they are done):

• Please resolve the existing merge conflicts
• Read https://github.com/jgrapht/jgrapht/wiki/How-to-make-your-first-%28code%29-contribution. There are still some things missing, such as the required headers in every class.
• "Replace the EdgeFactories with Suppliers (see the release notes from our latest release: EdgeFactories became deprecated)"
• "I noticed that some classes have fairly little javadoc in the class description. It might be useful to enhance that a bit as well (including links to external websites)."

[christophgruene]

IntervalGraphMapping is online