Correction for return codes, --systemd flag and fixes 2

This one is supposed to address issue #112 and it is a corrected version of #125.

It consists of:

    Add new enums for LSB return and status codes
    Make use of the above enums within autoip4, dhcp4, dhcp6, server, nanny, client
    Introduce --systemd common options for autoip4, dhcp4, dhcp6, server, nanny, client - this options is suppose to redirect log destination to syslog as well as suppress returning error codes systemd does not like.
    A few small fixes

Side note:
This time without ifup script changes... As agreeded with Marius this will follow later with support of ifreload and ifstatus based on wicked show + correct return codes.