Remove invalid releases automatically (#466)

Automatically remove empty releases or releases which are released in the future, regardless of the product.

Also refactored a bit releasedata.py to use better names and clarify types.

releases/notepad-plus-plus.json

@@ -1,33 +1,5 @@
 {
-  "releases": {
-    "8.8": {
-      "name": "8.8"
-    },
-    "8.7": {
-      "name": "8.7"
-    },
-    "8.6": {
-      "name": "8.6"
-    },
-    "8.5": {
-      "name": "8.5"
-    },
-    "8.4": {
-      "name": "8.4"
-    },
-    "8.3": {
-      "name": "8.3"
-    },
-    "8.2": {
-      "name": "8.2"
-    },
-    "8.1": {
-      "name": "8.1"
-    },
-    "7.9": {
-      "name": "7.9"
-    }
-  },
+  "releases": {},
   "versions": {
     "8.8.3": {
       "name": "8.8.3",