all: Fix various user-facing and non-user-facing typos (#8509)

Found via `codespell -q 3 -S lang,./gui/default/vendor -L benchs,bu,inflight,ro`

gui/default/syncthing/app.js

@@ -215,7 +215,7 @@ function buildTree(children) {
 
 // unitPrefixed converts the input such that it returns a string representation
 // <1000 (<1024) with the metric unit prefix suffixed. I.e. when calling this with
-// binary == true, you need to suffix an additon 'i'.  The "biggest" prefix used
+// binary == true, you need to suffix an addition 'i'.  The "biggest" prefix used
 // is 'T', numbers > 1000T are just returned as such big numbers. If ever deemed
 // useful 'P' can be added easily.
 function unitPrefixed(input, binary) {

gui/default/syncthing/core/syncthingController.js

@@ -2630,7 +2630,7 @@ angular.module('syncthing.core')
                                     noData: $translate.instant("There are no file versions to restore.")
                                 },
                                 // Set to '1' to silence errors after pressing arrow keys on file nodes.
-                                // Happens on the official option cofiguration from the developer's site
+                                // Happens on the official option configuration from the developer's site
                                 // too, so probably a bug?
                                 debugLevel: 1,
                                 source: buildTree($scope.restoreVersions.versions),

gui/default/vendor/fancytree/jquery.fancytree-all-deps.js

@@ -12900,7 +12900,7 @@ var uniqueId = $.fn.extend( {
 		},
 		// Overide virtual methods for this extension.
 		// `this`       : is this extension object
-		// `this._super`: the virtual function that was overriden (member of prev. extension or Fancytree)
+		// `this._super`: the virtual function that was overridden (member of prev. extension or Fancytree)
 		treeInit: function(ctx) {
 			var i,
 				n,
@@ -13715,7 +13715,7 @@ var uniqueId = $.fn.extend( {
 			}
 			// Add level-n class to apply indentation padding.
 			// (Setting element style would not work, since it cannot easily be
-			// overriden while animations run)
+			// overridden while animations run)
 			$(node.span).addClass("fancytree-level-" + level);
 			return res;
 		},