Automatically delete usage data older than set amount of time

Currently Zeitgeist stores all events indefinitely in the storage which can fill up the storage quite a bit . For now it is necessary to clear the usage data manually.

I propose therefore a feature to introduce a new option in the privacy manager which defines a time frame whenever an event has become older that defined time frame it will automatically delete it.

Example:
Users sets option to "Automatically delete usage data older than 30 days" and the privacy manager deletes the events which are older automatically in this case after 30 days.