* Fix a warning in PresetEditor line 806.
* Remove min_shell_thickness from the if condition in LayerRegion.cpp
* Add missing line in spiral vase check.
* Add initial set top shell thickness.
* Add minimum shell thickness for top/bottom layers.
* Some refactoring.
* Some Fixes.
* revert last change.
* a fix.
* Some refactoring.
* Some fix in calculating solid layers count.
* Refactoring in LayerRegion.cpp, Object.pm and PresetEditor.pm
* Added Minimum shell thickness option
-Added the option to libslic3r
-Created some of the necessary checks for illegal values
* Enforce min_shell_thickness as 0 when spiral vase is enabled
-This could be switched to match the extrusion width, but we already know there will only be 1 perimeter so this is probably more logical
* Feature is implemented
-Added a method in PerimeterGenerator to determine the amount of perimeters needed to meet min_shell_thickness
* Added a test in perimeters.t
* Fixed styling as requested
-Removed the magic number in PerimeterGenerator::num_loops()
-Added more test cases in perimeters.t
-Added documentation of the new feature in slic3r.pl and README.md
* Implemented requested changes
-Removed the num_loops function from PerimeterGenerator
-Added a scalled min_shell_thickness variable to PerimeterGenerator
-Changed the loop_number logic to use a previously defined variable loops
* Resolved more implementation issues
-Added min shell to invalidate state method
-Created additional checks in PresetEditor and LayerRegion for min shell
-Fixed the tooltip to be more descriptive
