Check for valid topic URL when publishing

Add domain whitelist

Update index page; mention websub, remove pubsubhubbub

use own user-agent header for http requests

Do not log HTTP errors when fetching topic for publishing

Forward duplicate headers to subscribers (especially Link headers)

s/PubSubHubbub/WebSub/

Delete outdated subscriptions

limit verification to 10 seconds

Ignore HTTP errors when verifying subscriptions

Fix errors related to missing default values

fix double slash

Subscriber count image

Disable test scripts by default

Remove subscription when subscriber returns "410 Gone"