More flexible and powerful refinement of variables in CA

...in/scala/leon/synthesis/condabd/SynthesizerExamples.scala

...a/leon/synthesis/condabd/refinement/VariableRefiner.scala

...synthesis/condabd/refinement/VariableRefinerCompose.scala

...nthesis/condabd/refinement/VariableRefinerExecution.scala

...nthesis/condabd/refinement/VariableRefinerStructure.scala

.../synthesis/condabd/refinement/VariableSolverRefiner.scala

.../scala/leon/test/condabd/enumeration/EnumeratorTest.scala

src/test/scala/leon/test/condabd/refinement/FilterTest.scala

...ala/leon/test/condabd/refinement/RefinementExamples.scala

.../test/condabd/refinement/VariableRefinerComposeTest.scala

...est/condabd/refinement/VariableRefinerExecutionTest.scala

...est/condabd/refinement/VariableRefinerStructureTest.scala

...n/test/condabd/refinement/VariableSolverRefinerTest.scala