squashed commit for changes that make mongodb_log work on groovy

moved conversion to a nicer place
(cherry picked from commit c7c92bbfe879a331a6fc9952f29f35821618ad56)

fixed issue with serialization of time stamps (genpy namespace), deactivated optimized tf logger for now
(cherry picked from commit 30939bb22d0f60621bb07c72ecb448335fa02eea)

Conflicts:

	src/mongodb_log.py

fixed tf recording with optimized C++ logger: convert path from list to string
(cherry picked from commit a7792fea7c7785f1c1eeb9aeeb78245687516a08)
Merge branch 'groovy-catkinzed' of github.com:marc-hanheide/mongodb_log into groovy-catkinzed