Bug 23834: Add default ESLint configuration

This patch adds a default ESLint configuration for use when editing
JavaScript, as recommended in the coding guidelines:

https://wiki.koha-community.org/wiki/Coding_Guidelines#JS8:_Follow_guidelines_set_by_ESLint

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

.eslintrc.json

@@ -0,0 +1,21 @@
+{
+    "env": {
+        "browser": true,
+        "jquery": true
+    },
+    "extends": "eslint:recommended",
+    "rules": {
+        "indent": [
+            "error",
+            4
+        ],
+        "linebreak-style": [
+            "error",
+            "unix"
+        ],
+        "semi": [
+            "error",
+            "always"
+        ]
+    }
+}