Fixed performance of forms refresh_custom_select
refresh_custom_select was looping twice thru the select options:
- once using $() to create the li elements
- then a second time trying to find the selected and disabled elements

this was causing the page to freeze when selects with many options were refreshed
instead the code was changed to construct the list's HTML with a string, and add
the selected and disabled classes at the same time if necessary.
Merge pull request #2934 from ziad-saab/forms-select-refresh-performance

Fixed performance of forms refresh_custom_select