Slicer3:Extensions:Directories

 Zip files downloaded to TemporaryDirectory (default: /Users/$USER/Slicer3$USER)
 Extensions installed to ExtensionInstallPath (default: /Users/$USER/Slicer3$USER/@SVN@)
 Slicer3 "default" extensions in Slicer3_INSTALL_MODULES_LIB_DIR