[th/initrd-move]

Move initrd code to src/nm-initrd-generator/.

Having the initrd generator code under src/core is not right. It is an independent tool of the daemon -- granted, it currently also uses

• libnm-platform code (only due to nmp_utils_modprobe(). We probably should move that away
• libnm-log-core to log to syslog, but it probably should print simply to stdout/stderr.

Anyway, aside those two dependencies (that it should not have), they are independent.