accidentally changed a jquery html to append, caused issues in single…

[cmcculloh-kr]

… select mode, fixed.

fixes #1589

[cmcculloh-kr]

I think a better solution than what we have now would be to remove the action columns header completely somehow, because there’s still two bugs going on here:

1. When all of the columns fit properly and the repeater doesn't need horizontal scroll, you still can scroll horizontally a little bit:
   

2. When all of the columns don't fit properly, and the empty placeholder is over a column's label, the label gets cut off:
   

However, this fix gets us a better overall experience in the short term.