added a Title field to slideshow Extra Fields
added hide/show switches for slideshow upload button
added a Link Title field to Extra Fields (slideshow)
if a slideshow is 'full'
  1) file upload button will disappear
  2) file drop area will be disabled

both are graceful to re-activate if the slideshow becomes no longer 'full'
Merge branch 'master' of https://github.com/punkave/apostrophe