Option to set default tag keys in tag editor

[mallniya]

As in foobar2000 it's convenient to have this option: instead of manually adding arbitrary meta key and set value, this feature reduces tag editing to just setting value for pre-baked key. Feature could be extended to also have full control of meta keys displayed by default in Selection info and Tag editor. For example, I don't use ALBUM ARTIST tag, so in this case this tag field is just a filler without a key in forementioned panels. In other words I'd better don't see this unused tag field by default and instead see it just as another non-standard tag field if tag exists at all.