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).

scripts/config.js

@@ -45,6 +45,7 @@ const symlinkFiles = [
 	'resource/ace/keybinding-emacs.js',
 	'resource/ace/keybinding-vim.js',
 	'resource/ace/mode-javascript.js',
+	'resource/ace/theme-chrome.js',
 	'resource/ace/theme-monokai.js',
 	'resource/ace/worker-javascript.js',
 	'update.rdf'