Introduce CSS lint

package.json

@@ -10,6 +10,7 @@
     "browser-test-remote-chrome": "nightwatch --config nightwatch.js --env chrome",
     "browser-test-remote-safari": "nightwatch --config nightwatch.js --env safari",
     "build": "mkdir -p build; browserify src/index.js -g yo-yoify -o build/app.js",
+    "csslint": "csslint assets/css/",
     "downloadsolc": "rm soljson.js; wget https://ethereum.github.io/solc-bin/soljson.js",
     "lint": "semistandard",
     "serve": "http-server ."
@@ -17,6 +18,7 @@
   "devDependencies": {
     "brace": "^0.8.0",
     "browserify": "^13.0.0",
+    "csslint": "^1.0.2",
     "es6-shim": "^0.35.1",
     "ethereumjs-abi": "^0.6.4",
     "ethereumjs-block": "^1.2.2",