tmf: Allow shift key to extend selection in time graph

tmf: Allow shift key to extend selection in time graph

- Extend the selection range when shift key is pressed while pressing
left or right keys.
- Extend the selection range when shift key is pressed while running the
next event, previous event, follow arrow fwd, follow arrow bwd actions.
- Update status line when the above actions modify the selection.
- Make sure the selection end time is visible when modifying the
selection range.
- Show status line when time graph control has focus with mouse outside
of the control bounds, but without displaying the cursor time.
- Highlight the selected state at the selection end time instead of the
selection start time.
- Remove the margin factor that made 'ensure visible' change the time
range when the selection was near the left or right margin.

Change-Id: Iee1dbbbc56e052de1a48bc638355e0c7dc126c2a
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/47381
Reviewed-by: Hudson CI