integrate release 3.1.1 to master
integrate release 3.2.0 to master
Merge branch 'feature-expl' into develop
initiate release 3.2.1
merging with version 3.2.1
Merge tag 'choco-3.2.1' into develop
Prepare the code for the next version
update scripts for release
update pom.xml
Merge branch 'feature-script' into develop
[EXPL] remove expl.add(aCause) from Propagator explanation

- Indeed, the ProapgatorActivation object offers the same service, and even more by explaining a propagator activation through reification, when needed.
- Fix #224: PropagatorActivation objects are needed, otherwise, the explanations are incorrect
- Remove PROP_IN_EXP in Configuration.properties (useless)