Avoid code repetition in the Problem Definition module

[Hector-hedb12]

We should review the code repetition in the ProblemDefinition subclasses and avoid it, moving the code to the parent class if it is necessary, the following methods need special attention:

• ProblemDefinition.generate_target_label(...)
• ProblemDefinition.generate_cutoff_times(...)

[ShahadThobaiti]

Fixed in PR #32