dataMgr:data: add two new methods.

1) Add lowestUpToDate() and highestUpToDate().
2) Add tests for these two new methods.

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>
strategy:turtle: add two new methods.

1) Add lowestUpToDate() and highestUpToDate().
2) Add tests for these two new methods.

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>