Ace: Config adjustments in Run JavaScript window

- Use the "Chrome" theme
- Hide the gutter
- Don't highlight the active line
- Remove default iframe borders
- Focus the editor on window open

Ace instances (e.g., Scaffold) are now responsible for setting their own
theme (to avoid a flash of Monokai before a lighter theme appears).

chrome/content/scaffold/scaffold.js

@@ -98,7 +98,11 @@ var Scaffold = new function() {
 		_editors.import = importWin.editor;
 		_editors.code = codeWin.editor;
 		_editors.tests = testsWin.editor;
-
+		
+		for (let i in _editors) {
+			_editors[i].setTheme('ace/theme/monokai');
+		}
+		
 		_editors.code.getSession().setMode(new codeWin.JavaScriptMode);
 		_editors.code.getSession().setUseSoftTabs(false);
 		// The first code line is preceeded by some metadata lines, such that