Update version to 1.2.0 and change Gecko ID in manifest.json; add .gitignore for web-ext-artifacts

.gitignore

@@ -0,0 +1 @@
+web-ext-artifacts/

manifest.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 2,
   "name": "vinted-favs-price",
-  "version": "1.1",
+  "version": "1.2.0",
   "content_scripts": [
     {
       "matches": ["https://www.vinted.de/member/items/favourite_list"],
@@ -10,7 +10,7 @@
   ],
   "browser_specific_settings": {
     "gecko": {
-      "id": "425f78c9-e49e-4346-a7b5-b03ce33ea526",
+      "id": "fav-price@vinted.de",
       "data_collection_permissions": {
         "required": ["websiteContent"]
       }