…idations. closes #350, related with #348, a part of #337

* error types now doesn't call methods from its struct fields for validation.
* remove isValid and Validate methods from types and adapt generic service.ValidateParametersSchema() method.
* TestValidParameters removed from service package. no longer needed.

…d error checking logic to parent caller

* TestCreateNotPresentEvent removed from event package, it has an equivalent TestEmitWrongEvent in interface/grpc/service.
* TestCreateInvalidData removed from event package, an equivalent TestEmitInvalidData added to interface/grpc/service.
* TestCreateInvalidTask removed from execution package, it has an equivalent TestExecuteWithInvalidTask in interface/grpc/core.
* TestCompleteNotFound removed from execution package, an equivalent TestSubmitWithNonExistentOutputKey added to interface/grpc/service.
* TestCreateInvalidInputs removed from execution package, an equivalent TestExecuteWithInvalidTaskInput added to interface/grpc/core.
* TestCompleteInvalidOutputs removed from execution package, an equivalent TestSubmitWithInvalidTaskOutputs added to interface/grpc/service.

…rent caller, re-add removed tests