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/dependency-track.json

@@ -1,27 +1,5 @@
 {
-  "releases": {
-    "4.9": {
-      "name": "4.9"
-    },
-    "4.8": {
-      "name": "4.8"
-    },
-    "4.7": {
-      "name": "4.7"
-    },
-    "4.13": {
-      "name": "4.13"
-    },
-    "4.12": {
-      "name": "4.12"
-    },
-    "4.11": {
-      "name": "4.11"
-    },
-    "4.10": {
-      "name": "4.10"
-    }
-  },
+  "releases": {},
   "versions": {
     "4.13.2": {
       "name": "4.13.2",