tmf: API clean-up of sequence diagram framework

tmf: API clean-up of sequence diagram framework

Throughout the sequence diagram framework, most member variables
were declared protected. However, in many cases getter and setter
methods exists and the member could have been declared private.
In some other cases, some of the attributes are internal data
and should not be be protected. This commit changes the modifier
of attributes to private. Getter and setter methods were added
where needed.

Change-Id: I7bf18335ff487c7a89b0d521e41b51e0bc3d1ad0
Signed-off-by: Bernd Hufmann <Bernd.Hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/12880
Tested-by: Hudson CI
Reviewed-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
IP-Clean: Alexandre Montplaisir <alexmonthy@voxpopuli.im>