Add SASSLint makefile target, and run it in CI

Also move ESLint and SASSLint config files to a dedicated .dev folder

.dev/.eslintrc.js

@@ -0,0 +1,12 @@
+module.exports = {
+  "extends": "airbnb-base",
+  "env": {
+    "browser": true,
+  },
+  "rules": {
+    "no-param-reassign": 0, // manipulate DOM style properties
+    "no-restricted-globals": 0, // currently Shaarli uses alert/confirm, could be be improved later
+    "no-alert": 0, // currently Shaarli uses alert/confirm, could be be improved later
+    "no-cond-assign": [2, "except-parens"], // assignment in while loops is readable and avoid assignment duplication
+  }
+};