moving boardhost to pxt

sim/visuals/boardview.ts

@@ -0,0 +1,19 @@
+namespace pxsim.visuals {
+    export function mkBoardView(opts: BoardHostOpts): BoardView {
+        if (opts.boardDef.visual === "microbit") {
+            return new visuals.MicrobitBoardSvg({
+                runtime: runtime,
+                theme: visuals.randomTheme(),
+                disableTilt: false,
+                wireframe: opts.wireframe,
+            });
+        } else {
+            let boardVis = opts.boardDef.visual as BoardImageDefinition;
+            return new visuals.GenericBoardSvg({
+                visualDef: boardVis,
+                wireframe: opts.wireframe,
+            });
+        }
+
+    }
+}