Feature/validators - MLTE-507, MLTE-150

[sei-secheverria]

Restructured Conditions to have a Validator inside that can guide the creation of the Condition, with specific arguments for bool expression, success message, etc, instead of depending on user of build_condition() figuring out the structure of the whole callback.

More specifically:

• Addresses Guide Creation of Condition Validation #507 by adding a Validator inside a Condition, and moving boilerplate code for validation inside Validator, leaving just a bool_exp as the lambda to be passed, separating success, failure, and info messages into own args
• Addresses Handle non-serializable Condition arguments when converting to/from JSON #150 by adding json_fix and loading it into internal wrapper json library to be used, which allows any class to implement the __json__() method and allow json.dumps to work when serializing it (it was applied to Artifact), but in theory people could add it to their own complex Condition arguments if needed).
• Also addresses Handle non-serializable Condition arguments when converting to/from JSON #150 by centralizing how JSON is created into a specific method in BaseModel, and creating specific exception for serialization errors
• Partially addresses Create Condition/Validator without creating/extending a type #508 by letting non-validator args of Condition be optional, in theory allowing the creation of Conditions directly without calling build_condition, but this is not clearly shown or explained in examples, nor fully tested in the unit tests yet, so it is mostly hidden. Functionality will be reviewed and clarified when Create Condition/Validator without creating/extending a type #508 is fully addressed in another PR.
• Renamed the "Ignore" result type into "Info", to more explicitly indicate that it is used to attach additional info, instead of indicating when it is used.
• Added missing unit tests for methods that build conditions
• Added sample image to be used in unit tests for Image class, instead of downloading image from the Internet, removing that dependency