Auth0 logout implementation

[balmas]

currently the AppAuthenticator uses the Auth0 Lock logout feature with a returnTo URL set to a logout page on the alpheios site. Need to explore the best solutions here across both desktop and mobile (and consistency with webextension)

[balmas]

We need to enable users of the embedded library to specify the redirectUrl for logout.

[balmas]

3rd party use of embedded library will not support auth in the MVP so moving this out of the release.

[irina060981]

Could be solved with #125