ENH: Create CLI Extension Wizard 'launcher'

Create a wrapper script to set up the environment (using the Slicer
launcher's --launcher-show-set-environment-commands) and execute the CLI
Extension Wizard via the appropriate Python interpreter. (Also, install
the Python application launcher wrapper for the same.)

This should provide a single, consistent mechanism for running the CLI
Extension Wizard (from a bash shell) from both build and install trees,
and regardless of whether system or Slicer-built Python is used. (On
Windows, git-bash must be used.)

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23294 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Pass template path to built wizard

Modify the build tree wrapper script for running the CLI Extension
Wizard to explicitly pass the template path for the built-in templates
(in the source tree). Since this script is configured anyway and only
used for the build tree, this is more straight forward than the trick we
use in the Extension Wizard module of parsing the CMakeCache.txt to find
the source directory.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23295 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Also check for installed templates

Modify SlicerWizard/ExtensionWizard.py to also look for the location to
which templates are installed (relative to its own install location) as
a default location for templates.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23296 3bd1e089-480b-0410-8dfb-8563597acbee