Add 'blc_command_forward_blc_channels' to make blc_command_loop automatically forward blc_channels without interpreting it

Separated blc_command in a new blc_loop. Make systemticaly athread to listen to the input ( avoid to block the program)

blc_command is now include by blc_program. blc_program_add_argument ask with a prompt the argument if it is needed but not set in commandline. This add somme warnings