COMP: Change "ScriptedLoadableExtensionTemplate" layout to support addition of modules.

As a side note, the ModuleWizard has been used to easily re-organize this
module (and also the one associated with r21745 and r21746):

Steps:
 1) cd /path/to/Extensions/Testing/ScriptedLoadableExtensionTemplate

 2) ../../Utilities/Scripts/ModuleWizard.py --template ./ScriptedLoadableExtensionTemplate/ --target ./ScriptedLoadableModuleTemplate ScriptedLoadableModuleTemplate

 3) mv ScriptedLoadableModuleTemplate/ ScriptedLoadableExtensionTemplate/

 4) Remove extra files

 5) Edit CMakeLists.txt and ScriptedLoadableModuleTemplate/CMakeLists.txt

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21747 3bd1e089-480b-0410-8dfb-8563597acbee
STYLE: In extension templates, change homepage url from 4.2 to Nightly

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21748 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Remove empty dirs

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21749 3bd1e089-480b-0410-8dfb-8563597acbee