Database statistics

- [x] New subpage with just the statistics
- [x] Total count of all media
- [ ] Total size of all media
- [x] Total tags count
- [ ] Display tags from the most frequent to least and in reverse
- [ ] Total length of video files
- [ ] Average size of all media and length of videos
- [x] Database creation date
- [x] Number of files compatible with the browser and files that aren't