Allow start_date, end_date, and URL in category schema

Add start and end date fields as well as URL to the category schema.
These properties are common across many categories supported here and
already present in a handful of data files.

This change also populates start and end date information based on the
recording dates in video files for a couple of categories that have
these fields present but do not pass the JSON Schema date format
validation.

References #268 and #1172.

Author: jonafato

.schemas/category.json

@@ -13,6 +13,20 @@
     "title":{
       "description":"Title of event where videos originated",
       "type":"string"
+    },
+    "url":{
+      "description":"Canonical URL to the event website",
+      "type":"string"
+    },
+    "start_date":{
+      "description":"Start date of the event in YYYY-MM-DD format",
+      "type":"string",
+      "format":"date"
+    },
+    "end_date":{
+      "description":"End date of the event in YYYY-MM-DD format",
+      "type":"string",
+      "format":"date"
     }
   },
   "required":[

djangocon-eu-2010/category.json

@@ -1,6 +1,7 @@
 {
   "description": "",
-  "start_date": null,
+  "start_date": "2010-05-24",
+  "end_date": "2010-05-26",
   "title": "DjangoCon Europe 2010",
   "url": ""
 }

pygotham-2012/category.json

@@ -1,6 +1,7 @@
 {
   "description": "",
-  "start_date": null,
+  "start_date": "2012-06-08",
+  "end_date": "2012-06-08",
   "title": "PyGotham 2012",
   "url": ""
 }