REST API: Include ID in post categories/tags

Also fixes type check so parent is included in categories

See https://github.com/Automattic/io/issues/64

Merges r106045-wpcom.
REST API: Rewrite publicize endpoints to allow for Jetpack support

Removes dependence on WPCOM-specific token retrieval

See: https://github.com/Automattic/beep-beep-boop/issues/122

Merges r106095-wpcom.
REST API: fix comment like properties typo in the return object code

see https://github.com/Automattic/io/issues/68
see https://[private link]#comment-2031

Merges r106096-wpcom.
Rest API: add background color data to site(s) endpoint

Merges r105447-wpcom.
REST API

Adjust some tests:
* check for our main test user binarysmash instead of gary for the groups test
* make sure themes's functions.php is loaded so we get the featured image support correct

Merges r105745-wpcom.
Revert part of r105745.  Lots of fatal errors.

Merges r105746-wpcom.
REST API

Adds new responses to help determine if a site is a mapped domain or not.
An additional response returns what the unmapped domain is (which can be used for preview URLs or other URLs where we don't care about the wp-admin piece being attached).

Merges r105921-wpcom.
REST API: allow geolocation metadata to be updated

Merges r105895-wpcom.
REST API: fix post thumbnail documentation

See https://github.com/Automattic/io/issues/64

Merges r106050-wpcom.
REST API: added missing private status

Merges r106085-wpcom.
REST API: Add publicize endpoint.