DO NOT MERGE Remove state handling duties from the base SeaNet driver

The SeaNet driver has been written to emulate a continuous scanning device while all the tritech
devices are polling-based. This led to a lot of state tracking, and makes the timeout specifications
close to useless (as the timeout for "read a scan" will actually be the timeout for "read a scan and
send a new command in some cases but not all ...).

There is very little complexity involved in pushing the duty of requesting scans to the class user (see the related pull request on the orogen component), and it simplifies the logic of the SeaNet class quite a lot.