Remco sync organisations

An issue with using the SSO server is that organisations don't exist yet in the client database until one of its users has logged in. This feature makes it possible to sync them using an API request that goes over the private network. Needs the pull request in -client.

I don't know why these API request use POST instead of GET, but that is a change I don't have time for now.
Waarom staat deze regel er nog, zo na de eigenlijke test?