made sure that we stay on active "slide" when elements are added to the head of the watched collection

While adding elements to the tail of the watched collection works fine, adding to the head has the undesired effect of also changing the active slide (since the element pointed to by the index changes when we add to the head of the collection). This commit compensates for this - BUT - not knowing all the details of the carousel implmentation - there might be corner cases im not aware of.. 
Any thoughts?