Upgrade to storybook 5

Fixes #184 (closed)

Migration 4->5

Upstream docs: https://github.com/storybooks/storybook/blob/master/MIGRATION.md#from-version-41x-to-50x

Storybook 5 changed how their URLs for stories are rendered, so the logic needed to be adjusted. e.g.:

iframe.html?selectedKind=base|badge&selectedStory=default

now looks like this:

iframe.html?id=base-badge--default

So it is a bit harder to extract the GlComponent name from that (e.g. GlBadge) than before.