Only handle tab key inside of editor

This refactors the controller a bit to insert 4 spaces when
a tab key is inserted inside of an editor, but in all other parts
of the app allow the user to use the tab key normally.

fix
https://github.com/standardnotes/desktop/issues/23

app/assets/javascripts/app/frontend/controllers/editor.js

@@ -15,8 +15,12 @@ angular.module('app.frontend')
 
       link:function(scope, elem, attrs, ctrl) {
 
-        var handler = function(event) {
+        /**
-      	  // Handle Tab Key
+         * Insert 4 spaces when a tab key is pressed, 
+         * only used when inside of the text editor.
+         */
+        var handleTab = function (event ) {
+
           if (event.which == 9) {
             event.preventDefault();
             var start = event.target.selectionStart;
@@ -25,6 +29,9 @@ angular.module('app.frontend')
             event.target.value = event.target.value.substring(0, start)
               + spaces + event.target.value.substring(end);
           }
+        }
+
+        var handler = function(event) {
           if (event.ctrlKey || event.metaKey) {
               switch (String.fromCharCode(event.which).toLowerCase()) {
               case 's':
@@ -56,6 +63,9 @@ angular.module('app.frontend')
         };
 
         window.addEventListener('keydown', handler);
+        var editor = document.getElementById("note-text-editor");
+        editor.addEventListener('keydown', handleTab);
+
 
         scope.$on('$destroy', function(){
           window.removeEventListener('keydown', handler);
@@ -100,8 +110,7 @@ angular.module('app.frontend')
 
     this.focusEditor = function(delay) {
       setTimeout(function(){
-        var element = document.getElementById("note-text-editor");
+        editor.focus();
-        element.focus();
       }, delay)
     }