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/debian.json

@@ -16,23 +16,14 @@
       "name": "6.0",
       "eol": "2014-05-31"
     },
-    "6": {
-      "name": "6"
-    },
     "5.0": {
       "name": "5.0",
       "eol": "2012-02-06"
     },
-    "5": {
-      "name": "5"
-    },
     "4.0": {
       "name": "4.0",
       "eol": "2010-02-15"
     },
-    "4": {
-      "name": "4"
-    },
     "3.1": {
       "name": "3.1",
       "eol": "2008-03-31"