Storybook with AmpImage

[sareh]

Describe the bug
A bug found as a result of this PR: #241

When running Storybook and going on the Amp Img stories, e.g. http://localhost:8080/?selectedKind=Image%20-%20AmpImg&selectedStory=16%3A9%20landscape%20image we get this console error:

To Reproduce
Steps to reproduce the behavior:

1. git checkout update-image-ampimg && npm run install:packages && npm run storybook
2. Click on http://localhost:8080/?selectedKind=Image%20-%20AmpImg&selectedStory=16%3A9%20landscape%20image Image should load
3. click on AmpImg Portrait image story. Image should load. Click on AmpImg Custom image story, Image does not load.
4. See error in console.

This is likely due to the AMP JavaScript being loaded multiple times.

Expected behavior
The Amp Img examples should load no matter how many times they are clicked on.

Desktop (please complete the following information):

• OS: Mac OS

• Browser & Version: Firefox nightly 66.0, Chrome canary 73.0

• Initially labelled with "bug"

[sareh]

Closed as fixed.