ENH: Part two of converting Registration chapter to ITKv4

In this part the Multi-resolution section is changed to reflect the new
characteristics of ITKv4 registration framework.
Also, a new section, called Multi Stage Registration" is added that
describes the ability of v4 framework to run several registration stages
consequently.

Change-Id: I15ba14945c65bede67a27bb76a92c40882ef970a