Apply leveled debug mechanism to wifimngr

The following debug functions can be used in wifimngr: wifimngr_err(...) wifimngr_warn(...) wifimngr_info(...) wifimngr_dbg(...)

Which are redirected to stderr based on the current wifi debug level: ERR_LEVEL (3) WARN_LEVEL (4) INFO_LEVEL (6) DBG_LEVEL (7)

@janusz @Marek @bartlomiej.grzeskowiak Please review.

Apart from adapting wifimngr into new leveled debug mechanism I have found after including wifimngr.h to wifimngr_event.c that wifimngr_event_register() had wrong declaration, so fixed it as well

Signed-off-by: Grzegorz Sluja grzegorz.sluja@iopsys.eu