Check data format of received frames

[ghost]

See: DataService class and implement the isDataFormatValid(...) method (it always returns true for the moment)
Tests are implemented, just implement and be sure that npm test is ok. They are marked as skipped for the moment on the console output:

Data Service
         Data Format

When isDataFormatValid(...) is implemented, please unskip them.
Proposal: use the jsonschema lib.