Server side transactions

[lvca]

Discussed in #117

^{Originally posted by lvca October 8, 2021}
Right now ArcadeDB HTTP/JSON protocol is totally stateless. This allows to use the transactions only with SQL scripts, but it's not the most user-friendly API to use.

I think the easiest thing to do is to bind a client session to a server-side session. On the server side, we could create a session id as a UUID and send it to the client at authentication as a token. If the client passes this token in the HTTP request header, then the server looks for the session id. In this way, we could save a transaction object and expose the begin + commit commands in the remote database API.