Migrate authentication library to oidc and refactor authentication code to separate service

[SlimShadyIAm]

Motivation

Citing cph-cachet/carp_studies_app#272, I have refactored the authentication code in carp_webservices to use the oidc library as it handles token refreshing and authentication more consistently and with a better API.

Closes #370, #371, #372

Changes

This PR makes the following changes:

• Use oidc for authentication
• Use offline tokens, which are refresh tokens that last much longer (currently configured to 30 days)
• Move authentication code out of CarpService into a separate CarpAuthService.
• Remove obsolete authentication methods from CarpService.
• Remove authentication-specific properties from CarpApp into a separate CarpAuthProperties class, which is usde to configure CarpAuthService.
• Migrate carp_backend so that it works with the new changes.
• Fixes If the app is opened without internet connectivity, the OIDC discovery document is not fetched, causing login to not work until app is restarted carp_studies_app#273 by re-initializing in the authenticate() method if the Login Manager is not initialized
• Example app now works (closes Example app not working in carp_webservices #350)

Breaking changes

• CarpApp had some properties removed which should now go into CarpAuthProperties, used to configure() CarpAuthService.
• In addition to configuring CarpService() in clients, CarpAuthService()also needs to be configured.

[bardram]

It all looks super good. Will create a separate branch and try the rest of the unit tests and then release the package.