Refactor statistics and add more features

[anorthall]

The statistics page and modules needs a complete re-write. It's an absolute train wreck. All functions should be abstracted into sensibly sized utilities. In addition to that, the following tasks should be completed:

• Show duration statistics
• Create a dedicated statistics page with more statistics
• Don't show statistics until a certain number of trips
• Show min/max/average trip length
• Optimise statistics code and make reusable template snippets
• Ensure that Surface trips are not counted in hours or distance - abstract to methods to count to ensure this
• Don't show blank statistics
• Show nights spent underground
• Implement pie charts for trip types by number of trips and time