Group artists starting with numbers and special characters

[Raphael0]

Part of a list of smaller enhancements, which I think could help polish the app:

Group artists starting with numbers and special characters as # in the artist list

Artists whose names start with a character that is not a letter (e.g. 1, 2, 3, %, &, ! ) currently get a new "header" created for each character. Since music collections will usually include few such artists, it would be cleaner to group such artists under a generic "#" header.

(now)

(suggestion)

[Raphael0]

Also, I would suggest to place artists starting with numbers or special characters at the end of the artist list, which seems more natural to me (but not all might agree)

[martpie]

yep, fair

[martpie]

Fixed in #939