Simply export all triangle meshes, do not apply boolean operations.
Change-Id: I91dda1d8a6805846fddcced7acccb43864c637e9
(cherry picked from commit 75e077f7a4204cd54380eeec37e930c01be1e3eb)
Previously grid infill may be cut, so the strength on one direction is too weak. Now we switch the order at neighboring layers, so the strength of both directions are good enough.
Change-Id: I0ba768eeee34ce430e43ea57d8f06c209d469d39