[demo-express] Merge 4 tests to demo express from usecase

- Merge Download, SystemInfo, SystemSettingIncomingCall and SystemSettingScreen to demo from usecase
- Download: Download folder default as N/A
- SystemSetting IncomingCall: No audio file default as N/A, click button adding error note
- SyttemSeting Screen: No picture file default as N/A, click button adding error note
[demo-express] Add 3 samples to demo express.

- Fail Reason: XWALK-2401, XWALK-2100

Impacted TCs num(approved): New 3, Update 0, Delete 0
Unit test Platform: [Tizen-IVI]
Unit test result summary: Pass 1, Fail 2, Blocked 0
Merge pull request #11 from xinliux/xinliux/merge-from-usecase

[demo-express] Merge 4 tests to demo express from usecase
Merge pull request #12 from JianfengXu/xujf/sample/add

[demo-express] Add 3 samples to demo express.