tmf: Add time graph marker axis for marker labels

tmf: Add time graph marker axis for marker labels

The marker labels are moved from the time graph scale to this bottom
axis.

There is one row of markers per marker category. Only the visible
categories with at least one computed marker are shown.

Clicking on a marker label sets the time selection to its time or range.

Mouse wheel over the marker axis can be used to zoom horizontally.

Change-Id: I7caf8168abd27fa9dac9e4729a4c1303775a81e6
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/66355
Reviewed-by: Hudson CI
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>