amp-base-carousel swipe slide transition issues

## What's the issue?

There are a couple of issues that we've found with the amp-base-carousel for swiping between slides:

- Sometimes the carousel will get randomly stuck and not allow the user to swipe left or right. Usually they'll have to wait 1-2 seconds before they can continue swiping through slides.
- The carousel will skip 1-2 slides depending on the user's swipe gesture (usually quick or long swipes does it).

## How do we reproduce the issue?
You can test on an iPhone device at the following URL:
https://az690879.vo.msecnd.net/7675/abc-issue.html

## What browsers are affected?

iOS Safari and iOS Chrome