Fix #582 sync blog visibility

Fix #582 sync blog visibility for wpcom users - also split wporg and wpcom login / fetch blog list calls.
Bonus: for wpcom users, auto select primary blog on login.

This PR must be tested against different wpcom and self hosted configurations:

* "normal" self hosted
* self hosted + self signed SSL
* self hosted + HTTP Auth
* self hosted + Jetpack
* wpcom + 2FA
* wpcom account with no blog
* wpcom with exactly one blog
* wpcom with two or more blogs


> Is it safe to assume that token will never be null here?

Yes, can't be null see :
https://github.com/Automattic/android-wordpress-com-rest/blob/ea667ce5752fd2f283f72a6428d383af2c2c034c/WordPressComRest/src/main/java/com/wordpress/rest/Oauth.java#L102
and
https://github.com/Automattic/android-wordpress-com-rest/blob/ea667ce5752fd2f283f72a6428d383af2c2c034c/WordPressComRest/src/main/java/com/wordpress/rest/Oauth.java#L163 (returns a constructor call).