[usecase-webapi] Improve Navigation Timing usecase

- Group the timing checkpoints in a div, add a a reload button.

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: Tizen M0
Tizen test result summary: Pass 1, Fail 0, Blocked 0
Merge pull request #623 from xinliux/xinliux/usecase/navigationtiming-improve

[usecase-webapi] Improve Navigation Timing usecase