Correct support for echo

[gnodet]

The echo support is completely broken.
When the terminal has echo enabled, normal processing should occur.
When the terminal has echo disabled, nothing should be printed.

The ConsoleReader.clearEcho() is a big hack in case the terminal can not be put into raw mode. But this is the responsibility of the client.
The client is either UnixTerminal or WindowsTerminal in case of a real console, but could be the ssh client. In the case of a remote terminal from ssh, the echo flag will always be set, but it should not mean that clearEcho should be used.

Ideally, we should also check and support echoctl, echonl flags.

[gnodet]

We should later deprecate Terminal.isEchoEnabled() in favour of a more generic getRawLocalFlags() returning the stty local flags of the terminal.