v0.6 - Improve clash detection and handling of large files

What's Changed

• Protection against memory spikes when downloading assets by @ababic in #31
• Automatic downsizing of larger-than-necessary images by @ababic in #32
• Fix: Occasional IntegrityError when saving 'new' assets by @ababic in #30

Full Changelog: v0.5.1...v0.6