ENH: Move the ClampImageFilter to the ImageIntensity module (#3016).

With the new feature allowing the ClampImageFilter to use
custom bounds, it makes more sense to have it in the
ImageIntensity module.

Change-Id: I411f36d19b64b2149b6cdcb6b0017397b848bd7b
Merge topic 'BUG3016-v5'

7aff84f ENH: Move the ClampImageFilter to the ImageIntensity module (#3016).