Allow POST via RestWS API

I really don’t understand why this was never enabled. It seems like it was purposefully left disabled with little to no explanation as to why.

Anyone can create a script that can login and then POST via a normal request using the fields from the form, for instance.

Enabling this would just make the process easier and consistent with the existing GET requests via the API (e.g. no extra “manual POST request” boilerplate code).