SLA support points improvements

- semi-intelligent algorithm to place support points
- enhanced ImGui dialog with editing/non-editing mode
- support points can have different head diameter (only implemented in GUI so far)
- autogenerated points supporting emerging islands are annotated and the info is kept

src/libslic3r/Model.hpp

@@ -12,6 +12,7 @@
 #include <utility>
 #include <vector>
 #include "Geometry.hpp"
+#include <libslic3r/SLA/SLASupportTree.hpp>
 
 namespace Slic3r {
 
@@ -175,7 +176,8 @@ public:
 
     // This vector holds position of selected support points for SLA. The data are
     // saved in mesh coordinates to allow using them for several instances.
-    std::vector<Vec3f>      sla_support_points;
+    // The format is (x, y, z, point_size, supports_island)
+    std::vector<sla::SupportPoint>      sla_support_points;
 
     /* This vector accumulates the total translation applied to the object by the
         center_around_origin() method. Callers might want to apply the same translation