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/slic3r/GUI/ImGuiWrapper.cpp

@@ -125,6 +125,12 @@ bool ImGuiWrapper::button(const wxString &label)
     return ImGui::Button(label_utf8.c_str());
 }
 
+bool ImGuiWrapper::radio_button(const wxString &label, bool active)
+{
+    auto label_utf8 = into_u8(label);
+    return ImGui::RadioButton(label_utf8.c_str(), active);
+}
+
 bool ImGuiWrapper::input_double(const std::string &label, const double &value, const std::string &format)
 {
     return ImGui::InputDouble(label.c_str(), const_cast<double*>(&value), 0.0f, 0.0f, format.c_str());
@@ -161,6 +167,26 @@ void ImGuiWrapper::text(const wxString &label)
     ImGui::Text(label_utf8.c_str(), NULL);
 }
 
+
+void ImGuiWrapper::combo(const wxString& label, const std::vector<wxString>& options, wxString& selection)
+{
+    const char* selection_u8 = into_u8(selection).c_str();
+
+    // this is to force the label to the left of the widget:
+    text(label);
+    ImGui::SameLine();
+    
+    if (ImGui::BeginCombo("", selection_u8)) {
+        for (const wxString& option : options) {
+            const char* option_u8 = into_u8(option).c_str();
+            bool is_selected = (selection_u8 == nullptr) ? false : strcmp(option_u8, selection_u8) == 0;
+            if (ImGui::Selectable(option_u8, is_selected))
+                selection = option_u8;
+        }
+        ImGui::EndCombo();
+    }
+}
+
 void ImGuiWrapper::disabled_begin(bool disabled)
 {
     wxCHECK_RET(!m_disabled, "ImGUI: Unbalanced disabled_begin() call");