[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
[wrt] update icon size from 117 to 128

[Detailed commit message (if have)]
Impacted TCs num(approved): New 0, update 0, deleted 0
Unit test platform: [tizen]
Unit test result summary:
 wrt-manifest-tizen-test:Pass 248, Fail 0, Blocked 0
 packagemgt/digitatlsign:pack to xpk install/uninstall/launch pass
Merge pull request #760 from linshen/shen/wrt/mainifest-117-128

[wrt] update icon size from 117 to 128
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
[wrt] Update test script to fix case bug in wrt-extension-android-tests
Merge pull request #761 from kangxu/kangxu/wrt/wrt-extension-android-tests/updateCase

[wrt] Update test script to fix case bug in wrt-extension-android-tests