[usecase-webapi] Update the description for usecase

- Update the description for usecase
[usecase-webapi] Improve Video for usecase

- Remove "For Tizen" and "For Android" in tests purpose
- PR-657 affect tests.tizen.xml and tests.android.xml, so update it again.

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 #713 from yunxliu/yunxliu/misc/spelling_mistake

[usecase-webapi] Update the description for usecase
Merge pull request #690 from xinliux/xinliux/usecase/video-update

[usecase-webapi] Improve Video for usecase