Squashed commit of the following:

Here is second version of the time measurement patch. First version is #919 and are to be closed.
* I have fixed all issues raised early, as well as have added execution time at gpx output.
* json output is now could contain "exec_time_ms":n as well as xml output has appropriate field at the metadata field.
* I have put measurement class into Util/TimingUtil.h, suppose it's more appropriate way to do measurement that existent one. We could discuss it here.