re-add postcss-loader

was mistakenly removed during merge of #824

Author: LinusBorg

template/package.json

@@ -97,6 +97,7 @@
     "nightwatch": "^0.9.12",
     "selenium-server": "^3.0.1",
     {{/e2e}}
+    "postcss-loader": "^2.0.8",
     "semver": "^5.3.0",
     "shelljs": "^0.7.6",
     "optimize-css-assets-webpack-plugin": "^3.2.0",