ENH: Remove "ITK" prefix from remote modules.

Remove "ITK" prefix from the remote module names. To better
distinguish remote modules from internal ITK modules.

DOC: Document the naming rules for remote modules.

The name of each remote module appear in itk_fetch_module()
function should be the same as the one defined in itk-module.cmake.
Also, the remote module names should not contain the "ITK" string
prefix.

MGHIO updates included in 841832fd94889d0793b606c0a5b9be981b98cec3
SCIFIO updates included in 67be5138c10769e2d9b09e96e2656ccf1d8c7a79
SmoothingRecursiveYvvGaussianFilter updates included in 0cc63e06fb4959a717527597d85dab8839d7176f

Change-Id: If7977d94b6ffd8ad690eef1f4558decbb851e425
Merge topic 'RemoteModuleNameConsistency'

bd382b5 ENH: Remove "ITK" prefix from remote modules.