Added throw/catch failure counter for OWL export

When the counter is != 0 after finishing an export, the number of failure throws didn't match the number of catches. This is a serious problem in semantics and will break the resulting output, so a warning in displayed in that case. If the warning isn't shown, everything is quietly assumed to be alright.
Reintroduced the global input lock for ROS service callbacks

To ensure that no race conditions happen, a global access mutex to all data structures accessed from ROS service callbacks is now in place. Service callbacks can now only be active one at a time, of any type (begin, alter, end context).