0.6.0

This release requires a database wipe due to new migrations.

• Add "Why digital technologies?" pīkau.
• Store and load readiness level for pīkau.
• Ensure pīkau title fits within pathway diagram nodes. (fixes #56)
• Fix bug where file licence warning displayed wrong licence. (fixes #60)
• Load file data from loader.
• Check files used in pīkau are listed within files application.
• Display links between files and pīkau. (fixes #61)
• Display image preview for files. (fixes #35)
• Add test cases.
• Dependency updates:
  • Update django from 2.0.5 to 2.0.6.
  • Update django-anymail 2.2 to 3.0.