Make tests using VMTK run in CircleCI

[olevs]

Tests using the VMTK extension currently need SlicerExtension-VMTK to be manually build. Fix the Docker-CircleCI setup so that tests needing several extensions run

• [x] Build SlicerExtension-VMTK in Docker image, and update Alive-Docker and Docker image
• [x] Check that the new Docker image works with the master branch - Ok, but Docker cashes everything, so Slicer didn't get updated from last image
• [x] Make tests include SlicerExtension-VMTK
• [x] Make CircleCI tests succeed - Replaced AdditionalLauncherSettings.ini with an alternative with SlicerExtension-VMTK path

[olevs]

Tested possible solutions for including Slicer extensions for ctest (not working):

• The default way of adding modules in Slicer is to use the GUI - Not possible in the Docker image
• The Slicer executable got an --additional-module-paths option, but I cannot get this to work with ctest
• When running "ctest -VV" it seems like the Slicer executable is run with the options --testing and --launch (among others) for running each test, but I cannot find a way of setting up all tests automatically
• The Slicer executable also got a --python-code option that can be used to run the function slicer.testing.runUnitTest, but I can't get this to work for running all tests either

The only solution that seems to (finally) work is to modify AdditionalLauncherSettings.ini in the Slicer-Liver build folder.