Add a heart beat variable which is published. Remove PubSub over Ethernet/UADP as simply not plans to use directly Ethernet directly.

Remove duplicating section just for the sake of name of the C compiler as by default gcc is a symbolic link which will point proper one.

See merge request nexedi/osie!14

Do not try to generate unique UUIDs as if they are used a human should do. Move code to a more re-usable file.

Allow to set arbitrary extra compiler flags from outside (usefull for supporting case when we need to disable x509 linking). Also by default do NOT link agains x509 / mbedtls.