291 clean up oauth mess (bitfireAT/davx5#307)

* Move GoogleOAuth members into GoogleLoginFragment

* Require login flow capable browser and notify user if missing

* Receive AppAuth redirects only in standard and gplay flavor

* Set davx5 as user-agent for AppAuth connection builder

* Re-authentication in Account settings

* Catch unauthorized exceptions at collection refresh and notify user to re-authenticate

* Suggest email address on account creation

* Set contact groups default setting as per-contact categories for oauth logins

* Add authentication to debug info, minor other changes

* Better error handling; don't pre-set group type

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Co-authored-by: Ricki Hirner <hirner@bitfire.at>