Link to artist entries for taken artist names.

In artist entries, there is a Check link next to the name field that
lets you check whether the name is already taken. When the name /is/
taken, you often want to check the other artist entries to see if
you're creating a duplicate. This adds links to the other entries so you
can check them more easily.
Merge pull request #2297 from evazion/feat-artist-check

Link to artist entries when artist name is taken.