Added maintenance script.
Added error checking for non-PubSubHubbub-enabled resources.
Fixed subscriber client test.
Refactored Subscription and added new test for Subscription::getAll().
Added tests for non-PubSubHubbub-enabled resource errors.
Added MWTimestamp instance to Subscription.
Merge branch 'develop' into feature/manage-subscription-maintenance
Fixed timestamps.
Added more details to the list of subscriptions.
Merge branch 'develop' into feature/manage-subscription-maintenance

Conflicts:
	src/SubscriberClient.php
	tests/phpunit/SubscriberClientTest.php
Fixed tests after merge.
Added error handling on unsubscribe request in case there is no active subscription.
Added unsubscription support to maintenance script.
Merge branch 'feature/manage-subscription-maintenance' into develop
Adapt code to new hooks.
Inserted callback for deletions.
Deleted useless TopLevelXMLHook.
Added secret field to Subscription model.
Added secret to POST data.
Added secret generation.
Merge remote-tracking branch 'origin/feature/hmac' into feature/xml-import

Conflicts:
	src/SubscriptionHandler.php