will be updated
Add parent class for Validation Tests

* Workflow now: each validation is defined by 2 classes that extend:
- ValidatioReport - stores the output of the validation test and some methods used for data representation
- ValidationTest (run method must be overloaded, run must return ValidationReport class type,
 some fields have to be updated)
- each validation is added to a list of validations which is further processed for yaml/html/console visualization

* updated unit tests corresponding to the changes
* added in Rake file: build, doc, test fields

Signed-off-by: Monica Dragan <monica.dragan@cti.pub.ro>