TransformedBoundaries and TransformedLogPrior don't override full interface

[MichaelClerx]

~In https://github.com/pints-team/pints/blob/master/pints/_transformation.py we have TransformedBoundaries and a TransformedLogPrior that implement some, but not all, of the methods in Boundaries and LogPrior. This means the remaining methods will return results using untransformed parameters.~

~E.g. the boundaries have a transformed range() method, but no transformed lower() or upper() methods. Neither class performs sampling.~

[MichaelClerx]

The Boundaries class doesn't define a range, upper, or lower, so the TransformedBoundaries shouldn't either

[MichaelClerx]

TransformedBoundaries is missing a sample method

[MichaelClerx]

Closed in #1450