Add the ability to periodically clean the recycle bin

On a busy wiki, deleted documents and attachments can pile up and take up storage space. We currently have a button to clean up the documents recyle bin, but it is a manual operation.

In order to make things properly manageable (and modern), we need a job that periodically cleans the documents and attachments recycle bin, based on configurable options. Here are some suggestions:

• how often to perform full cleanup OR
• how old are the entries in the recycle bin allowed to get OR
• how much storage space should the recycle bin sum up to

Optionally, as an advanced feature, we could also introduce a whitelist of documents/attachments for which never to clean up.