LastWill options

[Kuinox]

The last will currently will be sent only on the first reconnect.
In case of an automated reconnection, the last will won't be resent.
We should provide the following options:
Call user code to retrieve a new LastWill.
Resend the same last will everytime (imply we keep it in memory)
Forget it, so subsequent connect won't have it. (currently implemented).
There is no lastwill to send (currently implemented).