add ability to set default canvas by server

sort CanvasSelection list with default canvas first and linked canvases
after the canvas they link to

src/components/ModCanvastools.jsx

@@ -194,6 +194,7 @@ function ModCanvastools() {
     case 'makenull':
       // eslint-disable-next-line max-len
       descCleanAction = t`Turn every pixel in area to 0 (YOU REALLY SHOULDN'T DO THAT ON ANY AREA THAT ISN'T ALREADY MOSTLY 0)`;
+      break;
     default:
       // nothing
   }

src/components/windows/CanvasSelect.jsx

@@ -37,8 +37,19 @@ Archive of removed canvases can be accessed here:`} 
         >{t`Archive`}</span>
       </p>
       {
-        Object.keys(canvases).map((canvasId) => (
+        Object.keys(canvases)
-          (!canvases[canvasId].hid || showHiddenCanvases)
+          .sort((a, b) => {
+            // display forced default canvas first
+            if (a === window.ssv.dc) return -1;
+            if (b === window.ssv.dc) return 1;
+            // display linked canvas right after canvas they are linked too
+            // eslint-disable-next-line eqeqeq
+            if (canvases[a].linkcd != null) a = canvases[a].linkcd + 0.1;
+            // eslint-disable-next-line eqeqeq
+            if (canvases[b].linkcd != null) b = canvases[b].linkcd + 0.1;
+            return a - b;
+          }).map((canvasId) => (
+            (!canvases[canvasId].hid || showHiddenCanvases)
             && !canvases[canvasId].ed
             && (
               <CanvasItem
@@ -49,7 +60,7 @@ Archive of removed canvases can be accessed here:`}&nbsp;
                 selCanvas={selCanvas}
               />
             )
-        ))
+          ))
       }
       {
         (window.ssv?.backupurl

src/core/CanvasCleaner.js

@@ -120,9 +120,9 @@ const METHODS = {
     }
     return finPxl;
   },
-  
+
   makenull: (xc, yc, clrIgnore, canvasCleaner) => {
-    let pxl = canvasCleaner.getPixelInChunkArea(xc, yc);
+    const pxl = canvasCleaner.getPixelInChunkArea(xc, yc);
     if (pxl === null || pxl === 0) {
       return null;
     }

src/store/reducers/canvas.js

@@ -100,6 +100,9 @@ function getViewFromURL(canvases) {
 
   let canvasIdent = almost[0];
   let canvasId = getIdFromObject(canvases, canvasIdent);
+  if (!canvasId && window.ssv.dc) {
+    canvasId = window.ssv.dc;
+  }
   if (!canvasId || (!window.ssv?.backupurl && canvases[canvasId].ed)) {
     canvasId = DEFAULT_CANVAS_ID;
     const canvas = canvases[DEFAULT_CANVAS_ID];