Allow param overriding with kwargs in transform classes' __call__ (#141)

Summary:
Pull Request resolved: #141

Much simpler version of D31309584, to allow overriding transforms' kwargs in `__call__()`.

Reviewed By: jbitton

Differential Revision: D31570356

fbshipit-source-id: cc02ff3bfcc365fce3efe088b6eb2b9d45d6779d

Author: Zoe Papakipos