Make a Carousel Interval attribute for the carousel shortcode
This request it 2-fold:
-Allow site admins/editors to designate the interval between slide transitions, e.g [carousel interval= "20"] where 20 is the number of seconds between transitions.
-Allow site admins/editors to turn off transitions, so they do not happen automatically when the page loads, i.e. they only happen when a user clicks the arrows, e.g. [carousel interval="false"]