Removed multiuser. Added negotiation.

Xmpp now works with one user only, multyuser behaviour should be
implemented on top of it.

Added auth negotiation.

Refactoring.
Refactored see other host error handling.
The xmpp_gate module is refactored.
Small refactoring.
Now works in one process.

If request (or set of requests) is needed to be synchronous the socket
is supposed to be switched in passive mode and switched back to active
in waiting state.
Simplification in xmpp result.
Added logout and read (for push messages).

Negotiation steps are moved to xmpp_auth module.
Error checking and refactoring.
Added send_message and send_presence functions.
The xmpp_gate renamed to xmpp_request.

Related updates are done. Also the app file is updated.
Fixed issue with auth using user name and pass.

Also some refactoring is provided.
Added start/stop functions.
Fixed console output in xmpp:read function.
Fixed encoding issue.

The xmerl_scan module returns utf8 strings as unicode numbers if they
are bodies and as utf8 bytes (with reverse byte order) in case if they are
values of the items. So now it returns as unicode numbers in any case.
Directory structure reorganization.

Also xmpp:read method is renamed to handle_notification and removed
unused commented out code.
Added particular (incoming only) support of XEP-0085.