Don't reset showFaces every time a group is activated

Instead store the state separately for drawing and non-drawing group
types, and set showFaces to one of those, whenever a group is activated.

src/graphicswin.cpp

@@ -407,6 +407,8 @@ void GraphicsWindow::Init() {
     showEdges = true;
     showMesh = false;
     showOutlines = false;
+    showFacesDrawing = false;
+    showFacesNonDrawing = true;
     drawOccludedAs = DrawOccludedAs::INVISIBLE;
 
     showTextWindow = true;
@@ -1366,6 +1368,14 @@ void GraphicsWindow::ToggleBool(bool *v) {
         SS.GenerateAll(SolveSpaceUI::Generate::UNTIL_ACTIVE);
     }
 
+    if(v == &showFaces) {
+        if(g->type == Group::Type::DRAWING_WORKPLANE || g->type == Group::Type::DRAWING_3D) {
+            showFacesDrawing = showFaces;
+        } else {
+            showFacesNonDrawing = showFaces;
+        }
+    }
+
     Invalidate(/*clearPersistent=*/true);
     SS.ScheduleShowTW();
 }

src/group.cpp

@@ -416,11 +416,10 @@ std::string Group::DescriptionString() {
 }
 
 void Group::Activate() {
-    if(type == Type::EXTRUDE || type == Type::LINKED || type == Type::LATHE ||
-       type == Type::REVOLVE || type == Type::HELIX || type == Type::TRANSLATE || type == Type::ROTATE) {
-        SS.GW.showFaces = true;
+    if(type == Type::DRAWING_WORKPLANE || type == Type::DRAWING_3D) {
+        SS.GW.showFaces = SS.GW.showFacesDrawing;
     } else {
-        SS.GW.showFaces = false;
+        SS.GW.showFaces = SS.GW.showFacesNonDrawing;
     }
     SS.MarkGroupDirty(h); // for good measure; shouldn't be needed
     SS.ScheduleShowTW();

src/ui.h

@@ -802,6 +802,8 @@ public:
     bool    showEdges;
     bool    showOutlines;
     bool    showFaces;
+    bool    showFacesDrawing;
+    bool    showFacesNonDrawing;
     bool    showMesh;
     void ToggleBool(bool *v);