Clean-up Validation object

[HawaiianSpork]

• BaleenType.validate should return a Validation rather than a Sequence of ValidationResult. This will make it an O(1) operation to figure out wether the results are valid and other quick operations.
• No need to expose the Context, Data or DataTrace from the Validation object.
• Remove Context, it is just a container for a DataTrace + Data. We don't need another concept to confuse users.