swtbot: Add SWTBotTimeGraph and update SWTBotSash

swtbot: Add SWTBotTimeGraph and update SWTBotSash

The new classes SWTBotTimeGraph and SWTBotTimeGraphEntry are added to
better support UI testing of the time graph widget.

The class SWTBotSash is updated to simulate drag using SWT events.

SWTBot tests are updated accordingly.

Change-Id: Ic0800e73b85c624864825ab3f63e1bfadbacf945
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/85178
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>