Adding option for cxx_value for testing setting.

This parameter supersedes the generic value, just like the other
language specific values

Change-Id: Id20d1c8deb3282303e67f9a7524d2e3ed0c26769
Adding wrapping for the ImageNoise module

The tests are compared to noise free images with generous expected RMS error.

Change-Id: I0d7cf0a9a77ca7f5b2c4b75d57ec3ccac6781b19
Merge topic 'SIMPLEITK-542_AddImageNoiseFilters' into next

c13e423d Adding wrapping for the ImageNoise module
a38959bb Adding option for cxx_value for testing setting.