ENH: Adding MultiResolutionIterationEvent

This new event is derived from the IterationEvent, and used for
registration.

Change-Id: I2ea4ae8b0205743e93ab1f6bd314d3e559a31f81
Adding a Python example for multi-resolution BSpline registration

Change-Id: Ia7b7b6883e38f9f761bb6b03a606066fd7bc19b3
Adding baseline for new bspline example

Change-Id: I0b96e6f37c59e3600c2f86ea5cb81c0783f34647
Merge topic 'SIMPLEITK-571_AddMoreRegistrationExamples' into next

d9387b98 Adding baseline for new bspline example
f534cf8d Adding a Python example for multi-resolution BSpline registration
5d19a6f9 ENH: Adding MultiResolutionIterationEvent