Determine label color based on lowercase name

** What does this MR do? **
Determine the label color base on case-insensitive name

** Are there points in the code the reviewer needs to double check? **
Nothing special

** Why was this MR needed? ** 
Because when you have a label "Bug" it would not get the red bug color, since it would not match. With this fix, the label name would be downcased when parsing for color detection.

** What are the relevant issue numbers / Feature requests? **
Fixes: https://github.com/gitlabhq/gitlabhq/issues/6759