v2.6.2

- `New` Select all albums/photos with `cmd+a` or `ctrl+a`
- `New` Detect duplicates and only save one file (#48)
- `New` Duplicate photos (#186)
- `New` Added contributing guide
- `New` Database table prefix for multiple Lychee installations (#196)
- `Improved` Use IPTC Title when Headline not available (#216)
- `Improved` Diagnostics are showing system information
- `Improved` Harden against SQL injection attacks (#38)
- `Fixed` a problem with htmlentities and older PHP versions (#212)