Handle non-standard image types

[mikado2005]

Description

Allows ID3TagEditor to include APIC frames from MP3 files in which the image format is neither the standard jpg nor png format.

Motivation and Context

This allows user code to determine whether MP3 files contain images, and to access that image data even in non-standard formats.

How Has This Been Tested?

The existing XCODE test suite.

Types of changes

• [ ] New feature :sparkles: (non-breaking change which adds functionality)

Checklist:

• [ ] My change requires a change to the documentation :bulb: BUT I HAVE NOT yet updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document :busts_in_silhouette:.
• [ ] No new tests have been added.
• [ ] New code has been Swift linted.
• [ ] All new and existing tests passed :white_check_mark:.