Added support for for native OAuth login (#767)

[professorwaltwood]

PR for #767

First time contributing to iamb. Any issues or there's something I'm missing, please let me know

[VAWVAW]

Shouldn't this be the redirect_uri returned by LocalserverBuilder::build() to include the port?

[professorwaltwood]

iirc, oauth clients aren't restricted based off ports just scheme, host and path. Otherwise, for native clients like this, the client would need to re-register every time it needs to re-auth. This would also only work for dynamic client registration (should probably include an option in this PR for pre-registered iamb client)

[professorwaltwood]

not sure if it's limited to the oauth login method but when logging out, the crypto store isn't removed so on re-login, the client throws an error like this:
Failed to get OAuth login: Matrix client error: failed to read or write to the crypto store the account in the store doesn't match the account in the constructor: expected @professor:waltwood.dev:deviceid_1, got @professor:waltwood.dev:deviceid_2

[VAWVAW]

Another thing I noticed is that I can login with a different user id than I set in the config. We should set settings.profile.user_id = client.user_id() after session restore to make sure that we always have the right user. And we might make the user_id setting optional in a followup PR.

[VAWVAW]

Is there still something blocking this on your side? Otherwise I would like to merge this.