Change validateDefinition and validateSubmission to throw error and remove Results object

[nitro-neal]

Change these functions:

PresentationExchange.validateDefinition({ presentationDefinition })
PresentationExchange.validateSubmission({ presentationSubmission })

to throw an exception rather than return a results object if there is a problem with the submission or definition.

Optionally can refactor to:

PresentationExchange.validate(PresentationDefinition | PresentationSubmission) 

to make the api surface area even smaller