Increase granularity of artist tree

[Paul Lambert <paul at planar.id.au>]

Adds a new setting in the global settings of "Number of Artist Tree Groups". Allows you to have either the existing setting (A B C D E), or two letters per group (A B) or a single letter per group (A).

Ideally this patch would allow you to choose how many letters you wanted per group, but I wasn't confident enough with QString and unicode characters to try to dynamically create the array.

I note that this whole area of functionality might have unexpected behaviour if the first character of an artist's name is one from another alphabet - at present it looks like it would leave that artist out entirely. I can submit another patch for that if anyone thinks that is a real problem.

[anonymous]

Further investigation is that anything with non-English characters will end up in the other block at the top. That is probably OK.

[paulh]

(In [14751]) Increase the granularity of MythMusic's artist tree.

Adds a new setting in the global settings for "Number of Artist Tree Groups". Allows you to have either the existing setting (A B C D E), or two letters per group (A B) or a single letter per group (A).

I've split the General Settings into two pages and put the new setting on there with the Tree Sorting setting. Seems a more appropriate place for it to me.

Patch from Paul Lambert. Closes #4092.