Update slider loop functionality; fix keyboard control bug; add to styleguide docs

I have build upon @remybach 's "loopAround" functionality to bring it inline with the requirements of the hotels redesign. Default slider operation remains as before to keep it from breaking elsewhere on the site. In the process I discovered a small typo that kept the keyboard controls from working and fixed that. I also updated the slider's styleguide docs by adding reference to all the js parameter defaults. Previously it mentioned only `showSliderControls`. 


Squashed commits: 
Add at-loop-end class

Add check for loop end in updateCount to reset next button index

Update styleguide docs with slider loopAround

Fix keyboard controls bug

Add all js parameters to slider styleguide doc; set loopAround default back to false