v1.7

Changes in Sonic Annotator 1.7 since the previous release 1.6:

Front-end changes:

• Reinstate the ability to read mp3 files without file extensions.
  This was present (for all file types) up to v1.5. Support for
  reading mp3s in this way was removed in v1.6 because it caused
  problems with some other file formats but has now been restored
  with better checks.

General updates:

• Update the code to use Qt 6 and the current Sonic Visualiser
  libraries.