Changes to support Taiga 4.2.1

[swedishborgie]

Thanks for the excellent plugin! I recently had a need to integrate Taiga with Keycloak and this saved me a lot of effort.

I needed to make a few changes to make the plugin work correctly with Taiga 4.2.1:

• Added the ability to pass access tokens to the front end to support authenticating reverse proxies like keycloak-gatekeeper.
• Fixed several references to the Github contrib plugin.
• Fixed missing OpenID button image.
• Removed debugging print's.
• Updated documentation and change log.

Please let me know if you'd like any changes, and feel free to close this PR if you're not interested.

[robrotheram]

Thanks for that hard work. Its been on my list of things to fix