Code gardening and Javadoc update of Reaction class

[mcicolella]

Remove all issues reported by Sonarcloud and update Javadoc.

PLEASE BE CAREFUL BEFORE SENDING A PR

1. Double check every issue with great attention. Sonarcloud sometimes reports 'false' issues (e.g. unused variables but they are really used). In case of doubt ask our team
2. For Javadoc please follow the official style guide conventions http://www.oracle.com/technetwork/java/javase/documentation/index-137868.html
3. Review texts and fix typos and/or grammatical errors
4. Compile the code
5. Run the code to be sure there aren't runtime exceptions
6. If you want to propose a better implementation please add a comment describing your proposal of refactoring
7. Submit a PR with a single commit

NOTE: Don't remove "deprecated" methods.