split artist release credits role by comma with trim.

[state303]

Discogs dump presents data, not always but for some degree, , , as..

"Written-By, Producer"

which violates RDB point of view, such that it breaks query logics.

This can be fixed by using some custom logics from batch insertion,, such as

split(getDelimeters()).filter(removeBlank()).map(trimString()).distinct().toList();

Then we will have 2 distinct release credited artists.