Add the possibility to extract the front cover
image as binary data when the corresponding flag
This is probably how it should have been implemented from the beginning, and not how I did it in the embeddedimagedata class, which duplicates a lot of code and requires additional file operations.
Baloo can continue to work as is due to the new flags.
Taglib writer will follow if this is accepted. Afterwards, I will deprecate embeddedimagedata