Add stats page

[paul121]

It would useful from an administration perspective to be able to get a peek at the total # of previews as well as the current storage use/capacity. This is available from the tugboat dashboard but since it is available via their API as well I don't see why this couldn't be included at a dedicated endpoint on this site as well eg: /stats

• Preview count: https://api.tugboat.qa/v3#tag/Projects/paths/~1projects~1{id}~1jobs/get
• The project quota + current size is available here: https://api.tugboat.qa/v3#tag/Projects/paths/~1projects/get