Fixed issue with multiple CSS transitions

Fixed an issue with the transitions of the carousel, which failed to apply the `next`, `prev`, `left` and `right` classes when more than one CSS transition was set. This was due to multiple durations being returned as a comma-separated list (e.g. `".6s, 2s"`) which `slice(0, 1) * 1000` would turn into a `NaN`.

The fix adds another function, `findDuration`, to the `emulateTransitionEnd` flow, which returns the highest duration in the comma-separated list as milliseconds. The function won't interfere with existing uses, as integers are ignored.