More small fixes
Reduced z-index values. Fixes #608
Fix multiple issues

 - Fix issue with bs boxes
 - Fix issue with disabled first option followed by optgroup. Fixes #559
 - Fix issue with english text in code. Fixes #591
 - Fix select & deselect all to only work on visible items
   (liveSearch-aware)
Added new translation to english language
Refactoring less.
Refactoring less. Fix after rebase.