refactoring, tab switching handling shouldn't be on the widget level

src/public/app/components/note_context.js

@@ -105,11 +105,24 @@ class NoteContext extends Component {
         return appContext.tabManager.noteContexts.filter(nc => nc.ntxId === this.ntxId || nc.mainNtxId === this.ntxId);
     }
 
+    /**
+     * A main context represents a tab and also the first split. Further splits are the children contexts of the main context.
+     * Imagine you have a tab with 3 splits, each showing notes A, B, C (in this order).
+     * In such a scenario, A context is the main context (also representing the tab as a whole), and B, C are the children
+     * of context A.
+     *
+     * @returns {boolean} true if the context is main (= tab)
+     */
     isMainContext() {
         // if null, then this is a main context
         return !this.mainNtxId;
     }
 
+    /**
+     * See docs for isMainContext() for better explanation.
+     *
+     * @returns {NoteContext}
+     */
     getMainContext() {
         if (this.mainNtxId) {
             try {