tmf: Replace ITmfTimestamp by long in ITmfStatistics API

tmf: Replace ITmfTimestamp by long in ITmfStatistics API

Some methods in the statistics imlementations can call each
other, and having to create new wrapper objects every event
is not very interesting... The normalization already happens
in the Statistics view anyway.

Change-Id: I9769a867953d8f38dd2816ca7931b35dc22898a3
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/8650
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bhufmann@gmail.com>
IP-Clean: Bernd Hufmann <bhufmann@gmail.com>