Improvements definition of the icons.

Improvements in definition of the icons by user.
With this changes, now we can set icon per options/group.

Wiki/Doc:
To add the icon option:
- Add attribuite "uix-option-icon" to original select option.
To add the icon group:
- Add attribuite "uix-group-icon" to original select group.
  Note: Icon group will be applied only when CollapsableGroups = False
To add the collapse icon group:
- Add attribuite "uix-collapse-icon" to original select group.
To add the collapse icon group:
- Add attribuite "uix-expand-icon" to original select group.

Best Regards
Create jquery-multiselect-2.0.min.js
Changed to data-* attribuites

Changed to data-* attribuites
Changed to data-* attribuites

Changed to data-* attribuites
Always added class "ui-icon"

Always added class "ui-icon"
Always added class "ui-icon"

Always added class "ui-icon"
Merge pull request #32 from demonslord/master

Improvements in definition of the icons.