fix: inserted synchronize wrappers for methods of AbstractDocument to avoid ConcurrentModificationExceptions

Signed-off-by: marcel.dausend <marcel.dausend@uni-ulm.de>
fix: getRHS method returned first child of update rule instead of the right hand side term

Signed-off-by: marcel.dausend <marcel.dausend@uni-ulm.de>
added doxygen default configuration file
-needed doxygen
-proposed dot and mscgen
-maybe useful within eclipse - eclox eclipse plugin


Signed-off-by: marcel.dausend <marcel.dausend@uni-ulm.de>