Upgrade to monav 0.3, stay compatible with 0.2.

Use signals.h from monav 0.3 and favor that when both 0.2 and 0.3 are
installed. Migrate 0.2 maps to 0.3 at runtime if needed (just needs
a new config file).

Both versions can be mixed: You can run the daemon in version 0.2 and
load 0.3 maps as well as running daemon version 0.3 and loading maps
from 0.2. The other combinations as well of course.

Map updates on files.kde.org tbd.