_sim_pin was changed to pointer from array and length was checked with
strlen. If _sim_pin was null it caused crash. Fix by checking _sim_pin against NULL.
Power class could have been called without checking if power is NULL. Fix by checking
that power class is not null.
Fix state machine to return correct states when queried.
Moved methods to classes CellularDevice and CellularInformation.
SIM interface was removed to simplify cellular usage and
methods better suite new classes.
Updated greentea and unit tests.
Added check to state machine that if modem is attached to a network
it is considered to be registered to a network and state machine
can continue to next states. This fixed issues seen in IoT network
that network does not allow registering if already attached.
CellularDevice class own new state machine. Now we don't have to expose state machine
which may change and so we don't have to make API changes if that happens.
EasyCellularConnection uses now CellularDevice instead of old state machine.
Teppo Järvelin
Ari Parkkila