1) Let Clipper use int32_t for representing its coordinates. This
reduces memory and allows to skip conversion between Slic3r Polygon
and Clipper polygon.
2) Disable additional offset before executing the Clipper Offset algorithm.
We don't see any reason for that and it required 64bit Clipper coordinates,
which were disabled with 1).
Relies to:
Concentric Fill Start Point - New Feature Request #4948
Feature Request: Archimedean Chords - Option to define direction of travel (Inside-Out or Outside-In) #5214
Removed libslic3r from the default include paths for all modules but
libslic3r. Now headers from libslic3r need to be included with an
explicit path (libslic3r/libslic3r.h etc)
Split the localization macros into I18N.{cpp,h}
