Information removed from the cellular subsystem trace log:
* SIM pin
* APN username and password
Added get_debug() to ATHandler.h to get the current trace state in order
to support suspend/resume of trace output.
Change usage of AT_CellularContext::stack_type_supported to
AT_CellularBase::get_property. This way we can rid of
targets overriding stack_type_supported and delete
unnecessary classes and simplify new targets.
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.