[usecase-webapi] Improve Page Visibility usecase

- add description of locking screen/unlocking screen

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: [Andriod]
Test result summary: Pass 1, Fail 0, Blocked 0
Merge pull request #580 from zhangjingx/zhangjingx/misc/pagevisibility

[usecase-webapi] Improve Page Visibility usecase
[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
[misc-cordove] Improve cordova usecase description
Merge pull request #623 from xinliux/xinliux/usecase/navigationtiming-improve

[usecase-webapi] Improve Navigation Timing usecase
[wrt] Update suite name in xml for wrt-rtcoremanu-android-tests
Merge pull request #630 from kangxu/kangxu/wrt/wrt-rtcoremanu-android-tests/updateSuiteName

[wrt][XWALK-2241] Update suite name in xml for wrt-rtcoremanu-android-tests
Merge pull request #624 from wanghongjuan/wanghongjuan/misc/cordova-improve

[misc-cordove] Improve cordova usecase description