Prepare Protocol v25 init & authentication.

* TOSERVER_INIT and TOCLIENT_INIT renamed to _LEGACY
* TOSERVER_PASSWORD merged from dev-0.5, can use protocol v24 and v25
* TOCLIENT_ACCESS_DENIED merged from dev-0.5, can use protocol v24 and v25, with normalized strings an a custom id for custom errors
* new TOSERVER_INIT packet only send MT version, supported compressions, protocols and serialization, this permit to rework everything later without break the _INIT packet
* new TOSERVER_AUTH packet which auth the client
* new TOCLIENT_HELLO packet which send server serialization version atm
* new TOCLIENT_AUTH_ACCEPTED which is send when TOCLIENT_AUTH was okay. After this packet, the client load datas from servers, like after TOCLIENT_INIT_LEGACY packet