Use theme_item_list to take advantage of $attributes

Issue

Currently there is no way to add addition classes to a jcarousel.

Proposed Solution

Adding an attributes variable will help standarize the theme_jcarousel function with the core theme functions. It is also possible to use the theme_item_list function to build the unordered list so that theme_jcarousel will benefit from the theme_item_list function

Patch coming in comment