Decouple Slicing From Machine Frame Logic (#21)

* minor logic swap

* first attempt, has a race condition

* fixed the offset issue

* found a solution, I think things work now (at least once I quash this race condition)

* still chasing down race conditions

* add manual shear / scale order strategy swap

* tweak manual shear, fix ui uninitialization crash

* fix z height / g-code desync issue

* fix shear then scale cutoff planes

* getting closer

* fix support termination planes

* fix incorrect offsets in shear-then-scale mode

* test - fix overextrusion due to model/layer scale

src/libslic3r/CMakeLists.txt

@@ -221,6 +221,8 @@ set(lisbslic3r_sources
     GCode/AvoidCrossingPerimeters.hpp
     GCode/BeltBackTransform.cpp
     GCode/BeltBackTransform.hpp
+    GCode/MachineFrameTransform.cpp
+    GCode/MachineFrameTransform.hpp
     GCode/ConflictChecker.cpp
     GCode/ConflictChecker.hpp
     GCode/CoolingBuffer.cpp