More work on cadu format support.
Adapting server to cadu format.

Signed-off-by: Martin Raspaud <martin.raspaud@smhi.se>
Introduced multitimer.

Multitimer handles the problem of starting too many threads when using
timer objects to monitor the arrival time of new frames. Multitimer is just
one threads instead.

Signed-off-by: Martin Raspaud <martin.raspaud@smhi.se>
Main of cadu.py now receives frames instead of just reader.

Signed-off-by: Martin Raspaud <martin.raspaud@smhi.se>