Mostly mute CSSLint, re-enable gutter marks, hide squiggles

Only these rules are enabled:
* Parsing Errors
* Disallow empty rules
* Require use of known properties
* Require properties appropriate for display

codemirror/addon/lint/css-lint.js

@@ -18,6 +18,16 @@
 CodeMirror.registerHelper("lint", "css", function(text) {
   var found = [];
   if (!window.CSSLint) return found;
+
+  var rules = CSSLint.getRules();
+  var allowedRules = ["display-property-grouping", "empty-rules", "errors", "known-properties"];
+  CSSLint.clearRules();
+  rules.forEach(function(rule) {
+    if (allowedRules.indexOf(rule.id) >= 0) {
+      CSSLint.addRule(rule);
+    }
+  });
+
   var results = CSSLint.verify(text), messages = results.messages, message = null;
   for ( var i = 0; i < messages.length; i++) {
     message = messages[i];

edit.html

@@ -143,8 +143,8 @@
 			.applies-to img {
 				vertical-align: bottom;
 			}
-			.CodeMirror-lint-marker-warning {
-				display: none;
+			.CodeMirror-lint-mark-warning {
+				background: none;
 			}
 
 			@media(max-width:737px) {