BUG: Fix missing icons in extension manager

Update qSlicerBaseQTGUI.qrc[1] to include icons for new tool menu in
extension manager. This fixes the button for the same having no icon on
systems that lack the themed icon, as the non-themed icon was being
specified and exists in the source tree, but was missing from the
aforementioned .qrc.

(1: http://www.slicer.org/slicerWiki/index.php/Documentation/Nightly/Developers/Build_system/Qt_resource_files)

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23479 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Ensure MultiVolume modules work with VTK 5 and 6

This commit updates the modules to check for the version
of VTK (using `vtk.VTK_MAJOR_VERSION`). This is required
because the MacOSX factory is still building against VTK5.

For more details see:

  fedorov/MultiVolumeExplorer@1053c40
  fedorov/MultiVolumeImporter@351226a

From: Andrey Fedorov <fedorov@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23480 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Ensure extension wizard can find git executable provided by Git Bash

This commit explicit set the environment variable "GIT_PYTHON_GIT_EXECUTABLE"
to ensure GitPython finds and uses the git executable provided by Git Bash.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23481 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Properly serialize python paths when installing extension. Fixes #3772

Following r23036 environment variable specifying list of path were
handled differently. This commit ensures that python paths associated
with extension are also serialized into the settings by following the
new convention introduced in r23036.

For example, before this commit, after installing an extension named
"Foo", the settings contained:

// ----------------------
[Modules]
AdditionalPaths=/home/jchris/.config/NA-MIC/Extensions-23473/Foo/lib/Slicer-4.3/qt-scripted-modules

[...]

[EnvironmentVariables]
PYTHONPATH=/home/jchris/.config/NA-MIC/Extensions-23473/Foo/lib/Slicer-4.3/qt-scripted-modules
// ----------------------

whereas the following is now written:

// ----------------------
[Modules]
AdditionalPaths=/home/jchris/.config/NA-MIC/Extensions-23473/Foo/lib/Slicer-4.3/qt-scripted-modules

[...]

[PYTHONPATH]
1\path=/home/jchris/.config/NA-MIC/Extensions-23473/Foo/lib/Slicer-4.3/qt-scripted-modules
size=1
// ----------------------

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23482 3bd1e089-480b-0410-8dfb-8563597acbee