Documentation updates

[esune]

Resolves #408 , #409

Added basic documentation for mapper configuration, removed references to email-verification - now there is a dependency on the BC Wallet Showcase to obtain a demo credential.

[swcurran]

LGTM — verified that the identifiers match

[loneil]

Not sure why but tore everything down, got this branch and built fresh, and in the demo app to test I see
{"detail":"The requested verifier configuration wasn't found"}

Api is still getting a verified-email request from somewhere but I can't find it yet...

Never mind this. My local browser had a cached version of the vue app, incognito fixed it.

[loneil]

I started this up fresh locally, added the showcase cred config with curl, got a showcase cred on my phone through the link, and ran through the Vue demo and it works for me. 👍