Exceptions thrown by Flow calculation were made explicit classes derived
from std::invalid_argument.
The PresetHints::recommended_thin_wall_thickness() newly catches these
exceptions and it shows the reason of why the hint is invalid.
The two new config keys define a minimum vertical shell thickness.
The top shell thickness is calculated as a maximum of sum over
top_solid_layers * layer heights and top_solid_min_thickness,
the bottom shell thickness is calculated as a maximum of sum over
bottom_solid_layers * layer heights and bottom_solid_min_thickness.
The results of the formula above are shown at the Print parameter page
below the two new values to hint the user about the interaction
of the old versus new config values.
top_solid_min_thickness has no meaning if top_solid_layers is zero,
bottom_solid_min_thickness has no meaning if bottom_solid_layers is zero.
Export of the names of the SLA profiles was performed into the config bundle
for SLA profiles, which were nop set. A safe method is now used,
which stores an empty string in such a case.
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}
