Add LowerLayerSetter class to allow to tweak coap level parameter for requests

[sbernard31]

This aims to implements #875.

An example of use :

// configure reliability parameters
Builder reliabilityParams = ReliabilityLayerParameters.builder();
reliabilityParams.ackRandomFactor(1).ackTimeout(100).ackTimeoutScale(1).maxRetransmit(1);
// send requests
ReadResponse response = server.send(registration,
                                    new ReadRequest("3/0/1"),  
                                    CoapRequestSetter.reliabilitySetter(reliabilityParams), 
                                    timeout);

[sbernard31]

The master version (without any backward compatibility stuff and with support for bootstrap server is available at 7a2966a)

[msangoi]

WDYT of LowerLayerConfig? with an apply() method

[sbernard31]

👍 sounds good. I will modify it.

[sbernard31]

This now integrated in branch 1.x (cf7dbc9 ) with backward compatibility
and in master commit (813d664) without backward compatibility.