tmf.ui: use binary search when adding child to TimeGraphEntry

tmf.ui: use binary search when adding child to TimeGraphEntry

This brings the search time complexity to O(log(n)) down from
O(n).

Change-Id: I5b97c0f341bfe712d1bb8f9fd95cffc9ccd8686c
Signed-off-by: Loïc Prieur-Drevon <loic.prieurdrevon@gmail.com>
Reviewed-on: https://git.eclipse.org/r/86000
Reviewed-by: Hudson CI
Reviewed-by: Jonathan Rajotte Julien <jonathan.rajotte-julien@efficios.com>
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>