ENH: expose parameter in Bilateral filter

This commit addresses JIRA issue #2996.

The parameter m_DomainMu from the BilateralImageFilter is exposed.

Moved the constructor implementation to the hxx.

Updated the tests to specifically set m_DomainMu, to test this function.

Change-Id: I1c80ae6abe067d6ae8b4f61a95cef6432db38036
Merge topic 'BilateralFilter'

fd2fab1 ENH: expose parameter in Bilateral filter