Fix bad "mailto:" linkes generated by Add Link dialog.

The code I've edited, at
core/app/assets/javascripts/refinery/admin.js.erb:510,
converts a "mailto:" recipient email address from ascii format to
hexadecimal-encoded. Unfortunately this encoding doesn't work for all
browsers. I think this might be a security/input-sanitizing measure,
so I'm hesitant to undo it; but since it doesn't work for me, it's
useless.

I'll need to do some research to find the correct way of sanitizing this
link.