Benchmarker should support custom reading and writing of solutions (it should not enforce 1 specific xstream configuration)

Title was: Benchmark doesn't allow for de-serializing XMLs with references

I have a solution configuration serialized via XStream [1]. When I'm attempting to benchmark [2] my solver with that solution, I get the following error:

[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2:java (default-cli) on project tournaments: An exception occured while executing the Java class. null: InvocationTargetException: Problem reading unsolvedSolutionFile: src/main/resources/input-tiny.xml: Invalid reference
[ERROR] ---- Debugging information ----
[ERROR] reference : ../../group
[ERROR] class : org.drools.planner.examples.tournaments.model.Team
[ERROR] required-type : org.drools.planner.examples.tournaments.model.Team
[ERROR] converter-type : com.thoughtworks.xstream.converters.reflection.ReflectionConverter
[ERROR] line number : 22
[ERROR] class[1] : org.drools.planner.examples.tournaments.TournamentsSolution
[ERROR] version : null
[ERROR] -------------------------------

I can see two solutions:
a) Make it so that Planner benchmark does understand XStream's XML.
b) Provide a method inside Planner to serialize Solutions in a way that benchmark will understand them later.

References:
[1] https://github.com/triceo/Drooling-Tournaments/blob/master/src/main/resources/input-tiny.xml
[2] https://github.com/triceo/Drooling-Tournaments/blob/master/src/main/resources/benchmarkConfig.xml
[3] https://github.com/triceo/Drooling-Tournaments