Catched 2 bugs I produced

Redone the `bs_nav_item` function:

* sprintf of course, I love it.
* eliminated possible output of empty class=""
* I used the `str_replace` on the `$content` before running it through `do_shortcode` so we can check for the actual shortcode rather then for every possible `ul`. Thats thats the best I can come up with now. I think its fine but still feels a bit hacky.
* I had this idea if switching pattern based on if we have dropdown but that would not work this way. There could be a attribute for the dropdown link text/html(yeah I think shotcode can even take html) for doing it this way but I not really would like this.