Register the control flow as selection provider

Register the control flow as selection provider

In order to signal the selection of a task in the control flow view,
register the tree view in the selection service. It allows other
plug-ins to listen for selection change.

Signed-off-by: Francis Giraldeau <francis.giraldeau@gmail.com>
Change-Id: I5294e12c660c60a8e01f1b76c3e993da6e6534af
Reviewed-on: https://git.eclipse.org/r/10115
Tested-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
IP-Clean: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
IP-Clean: Alexandre Montplaisir <alexmonthy@voxpopuli.im>