Fix #1368 menu hover texts say "undefined"

Fix #1367 Incorrect cursor in prism editor
Fix #1370 Cant recover some keyframes with undo when they were overlapping

css/prism.css

@@ -21,6 +21,7 @@ pre[class*="language-"] {
 	word-break: normal;
 	word-wrap: normal;
 	line-height: 1.5;
+	cursor: text;
 
 	-moz-tab-size: 4;
 	-o-tab-size: 4;

js/animations/timeline.js

@@ -911,7 +911,6 @@ Interface.definePanels(() => {
 							}
 							Blockbench.setStatusBarText();
 							if (values_changed) {
-								Undo.addKeyframeCasualties(deleted);
 								Animation.selected.setLength();
 								Undo.finishEdit('Drag keyframes');
 							} else {

js/interface/interface.js

@@ -606,7 +606,9 @@ $(document).keyup(function(event) {
 Interface.createElement = (tag, attributes = {}, content) => {
 	let el = document.createElement(tag);
 	for (let key in attributes) {
-		el.setAttribute(key, attributes[key]);
+		if (attributes[key] !== undefined) {
+			el.setAttribute(key, attributes[key]);
+		}
 	}
 	if (typeof content == 'string') el.textContent = content;
 	if (content instanceof Array) {