babeltrace lib cleanup, folded with open/remove trace functions

Folded patch from Yannick Brosseau <yannick.brosseau@gmail.com>, along
with various updates and cleanups, related to babeltrace lib.

Original changelog from Yannick Brosseau:
	Move the trace_collection into its own file.
	Port the converter to uses the new functions

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>