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/rtpengine.json

@@ -1,30 +1,5 @@
 {
-  "releases": {
-    "13.4": {
-      "name": "13.4"
-    },
-    "13.3": {
-      "name": "13.3"
-    },
-    "13.2": {
-      "name": "13.2"
-    },
-    "13.1": {
-      "name": "13.1"
-    },
-    "13.0": {
-      "name": "13.0"
-    },
-    "12.5": {
-      "name": "12.5"
-    },
-    "11.5": {
-      "name": "11.5"
-    },
-    "10.5": {
-      "name": "10.5"
-    }
-  },
+  "releases": {},
   "versions": {
     "13.4.1.1": {
       "name": "13.4.1.1",