more mem optimizations: poly length/area. worker now cleans up widget groups

src/kiri/main.js

@@ -2872,7 +2872,7 @@
                 complete = {};
                 UI.back.style.display = '';
                 UI.render.style.display = '';
-                // KIRI.work.clear();
+                KIRI.client.clear();
                 STACKS.clear();
                 hideSlider();
                 updateSpeeds();

src/kiri/widget.js

@@ -123,6 +123,10 @@
                 }
             });
             return bounds;
+        },
+
+        clear: function() {
+            groups.length = 0;
         }
     };
 

src/kiri/worker.js

@@ -47,6 +47,7 @@ KIRI.worker = {
         current.print = null;
         dispatch.group = wgroup = {};
         dispatch.cache = wcache = {};
+        KIRI.Widget.Groups.clear();
         send.done({ clear: true });
     },
 
@@ -162,6 +163,8 @@ KIRI.worker = {
     slice: function(data, send) {
         send.data({update:0.001, updateStatus:"slicing"});
 
+        current.print = null;
+
         let settings = data.settings,
             widget = wcache[data.id],
             last = time(),