Took a whack at cleaning up old blobs.

git-svn-id: https://www.unprompted.com/svn/projects/tildefriends/trunk@4369 ed5197a5-7fde-0310-b194-c3ffbd925b24

core/core.js

@@ -72,6 +72,16 @@ const k_global_settings = {
 		default_value: undefined,
 		description: 'Comma-separated list of host names to which HTTP fetch requests are allowed.  None if empty.',
 	},
+	blob_fetch_age_seconds: {
+		type: 'integer',
+		default_value: undefined,
+		description: 'Only blobs mentioned more recently than this age will be automatically fetched.',
+	},
+	blob_expire_age_seconds: {
+		type: 'integer',
+		default_value: undefined,
+		description: 'Blobs older than this will be automatically deleted.',
+	},
 };
 
 let gGlobalSettings = {