Rulekit

Fixed very rare bug of model being dependent on the order in the nominal attribute mapping.

* Migrate to latest RuleKit jar file v1.7.4
* Fix issue 20

Fixed issues:
* Issue 17 java.lang.NullPointerException during expert rule induction
* Issue 19 java.lang.java.lang.RuntimeException when inducing rules on DataFrame with boolean columns

* Move test dependencies to the `./tests/requirements.txt` file.
* Loosen depencencies versions requirements