ENH: Import BModeImageFilter.

From:

  https://www.gitorious.org/ultrasound-b-mode/b-mode/source/05623d5f16d98ba32427ec9cee363f62566aa9b0:
ENH: Add BmodeImageFilterTestTiming.

From:

  https://www.gitorious.org/ultrasound-b-mode/b-mode/source/05623d5f16d98ba32427ec9cee363f62566aa9b0:

Also add RegionFromReferenceImageFilter, required by BModeImageFilter.

Update BModeImageFilter to use AddImageFilter instead of
AddConstantImageFilter.

Fix shadowed padding variable.
ENH: Add BMode baseline comparison.
BUG: Add missing ITK_TEST_OUTPUT_DIR to test file paths.
BUG: Fix Doxygen group for new classes.
STYLE: Fixes for BModeImageFilter, RegionFromReferenceImageFilter.