Refactoring the rationals library.

Separated ExtendedRational into two classes:
Rational and ExtendedRational, wrapping the former.

Conflicts:
	src/org/sosy_lab/cpachecker/core/counterexample/AssignmentToEdgeAllocator.java
	src/org/sosy_lab/cpachecker/cpa/stator/policy/LinearConstraintManager.java

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14366 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c