Queue wrapper: add function to release events associated with queue

cf4ocl command queue wrappers internally keep events for profiling
purposes and simpler handling of event associated memory. However,
a very large number of events can have an impact on utilized memory.
In such cases, this function can be used to periodically release
these events.
Several additions to the profiler module

- Add command type to event info
- Add functions to get duration of all OpenCL events
- Release command queue events after profiling