ctf: Assign a CtfTmfEventFactory to each trace

ctf: Assign a CtfTmfEventFactory to each trace

A singleton factory means we cannot possibly extend CtfTmfEvent,
because the sole factory can only generate CtfTmfEvent objects.

To rectify this, we can turn the factory into a standard non-static
class, and have each trace take ownership of its event factory. This
means that sub-classes of CtfTmfTrace will be able to provide their
own extension of CtfTmfEventFactory if they want to generate other
event types.

Bug: 476679
Change-Id: I66e9cd49044edd2a77276d779d0f563a2e20d520
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/56191
Reviewed-by: Hudson CI