COMP: Fix UseTubeTK.cmake inclusion of Slicer4Config.cmake

Slicer4Config.cmake needs to know the location of SlicerExecutionModel_DIR
so we include it after it is set.

Change-Id: I7981f9b83bb9b7e1402aef3fb8e20fa72aa04319
Merge topic 'UseTubeTKSlicer4Config'

48ee4e5 COMP: Fix UseTubeTK.cmake inclusion of Slicer4Config.cmake