ENH: add SegmentationAdiedRegistration extension s4ext

this module is able to perform registration of two grayscale images. In particular, when we want high registration accuracy at certain organ, we can segment them and use the binary masks to aid the registration.
ENH: figures redirected to namic wiki to avoid https on github
STYLE: two figures moved to slicer wiki, module wiki still on na-mic wiki coz i'm not sure where on slicer wiki this should fit to...
STYLE: module home page changed to slicer wiki
Merge pull request #334 from gaoyi/add-SegmentationAidedRegistration

ENH: add SegmentationAdiedRegistration extehttp://www.slicer.org/slicerWiki/index.php/Documentation/Nightly/Modules/SegmentationAidedRegistrationnsion s4ext