magnetometer msg check: isnan() -> !isfinite()

This catches both inf and NaN. Not sure whether sending inf in a Vector3
message is valid (Nan is), but this doesn't hurt and is just good
defensive programming.
check for NaNs in magnetometer message

Some magnetometer drivers (e.g. phidgets_drivers) output NaNs, which
is a valid way of saying that this measurement is invalid. During
initialization, we simply wait for the first valid message, assuming
there will be one soon.
reconfigure server: use proper namespace

Before, the reconfigure server used the private namespace of the nodelet
*manager* instead of the nodelet, so the params on the parameter server
and the ones from dynamic_reconfigure were out of sync.
gain and zeta already set via dynamic_reconfigure

Reading the params explicitly is not necessary. Instead,
dynamic_reconfigure will read them and set them as soon as we call
config_server_->setCallback().
turn mag_bias into a dynamic reconfigure param

Also rename mag_bias/x --> mag_bias_x etc., since dynamic reconfigure
doesn't allow slashes.
add me as maintainer to package.xml