[usecase-webapi] Improve Systemsetting screen usecase.

- Add precondition before test to the info area after click the 'info' button.
- Remove section title for "Get HomeScreen/lockscreen image, canvasimage".
- Draw a frame to show HomeScreen image or LockScreen image.

Impacted tests(approved): New 0, Update 1, Delete 0
Unit test platform: [Tizen m0]
Unit test result summary: Pass 1, Fail 0, Block 0