Apply cursor styles during paint

This makes the editor's cursor an IBeam and properly deals with nested cursor styles.

Co-Authored-By: Antonio Scandurra <me@as-cii.com>

styles/src/styleTree/selectorModal.ts

@@ -50,10 +50,6 @@ export default function selectorModal(theme: Theme): Object {
         top: 7,
       },
     },
-    margin: {
-      bottom: 52,
-      top: 52,
-    },
     shadow: shadow(theme),
   };
 }

styles/src/styleTree/workspace.ts

@@ -75,6 +75,13 @@ export default function workspace(theme: Theme) {
     leaderBorderWidth: 2.0,
     tab,
     activeTab,
+    modal: {
+      margin: {
+        bottom: 52,
+        top: 52,
+      },
+      cursor: "Arrow"
+    },
     leftSidebar: {
       ...sidebar,
       border: border(theme, "primary", { right: true }),