Add j2kH & cdef Box definitions

[dukesook]

The 'j2kH' box:

• is named the J2KHeaderItemProperty or J2KHeaderInfo box.
• is a superbox, which means that it only contains other boxes
• is defined in ISO/IEC 15444-16
• is used to store JPEG 2000 metadata

The 'cdef' box:

• is named the Channel Definition box.
• is defined in ISO/IEC 15444-1.
• shall be present in the j2kH box.
• Provides channel information. (RGB, Grayscale, YCC, etc.)

[dukesook]

@cconcolato Can you review this?

[dukesook]

Thank you!

[dukesook]

@cconcolato Here is a copy of 15444-16:2021.