necessary changes for the latest DeviceAccess update (readAsync() return type no longer a reference, and other related changes)

Changed an exception into an assert, since the function is only internally used and the exception is never thrown. Clafiried the documentation about this.

- check if connections are actually working

removed incorrect implementation of operator[] and operator() in ApplicationModule (and use the implementations of ModuleImpl instead)

don't catch the exception thrown when we cannot obtain the testable mode lock, this is no longer necessary as all threads will obtain the lock at the beginning

excluded some more assert-like exceptions from coverage report and changed one into an actual assert

reduced the timeout for stall detection of testable mode to 1s, which should be perfectly long enough