refdebug: Create refstats.py script.

This allows us to process AO2 statistics for total objects, memory
usage, memory overhead and lock usage.

* Install refstats.py and reflocks.py into the Asterisk scripts folder.
* Enable support for reflocks.py without DEBUG_THREADS.

Steal a bit from the ao2 magic to flag when an object lock is used.
Remove 'lockobj' from reflocks.py since we can now record 'used' or
'unused' for those objects.

Add comments to explain thread safety of the 'struct __priv_data'
bitfields.

Change-Id: I84e9d679cc86d772cc97c888d9d856a17e0d3a4a