Add 4 samples to demo express.

- Fail Reason: XWALK-2401, XWALK-2100, SSO: clearDB method error.

Impacted TCs num(approved): New 4, Update 0, Delete 0
Unit test Platform: [Tizen-IVI]
Unit test result summary: Pass 3, Fail 1, Blocked 0
config 12 samples in xml.
Merge 4 tests to demo express from usecase

- Merge Download, SystemInfo, SystemSettingIncomingCall and SystemSettingScreen to demo from usecase
Move usecase to demo-express

- Move usecase to demo-express
- Failure analysis: https://crosswalk-project.org/jira/browse/XWALK-1954
                    https://crosswalk-project.org/jira/browse/XWALK-1266

Impacted tests(approved): new 0, update 4, delete 0
Unit test platform: [Tizen IVI]
Unit test result summary: pass 2, fail 2, block 0
Add CordovaMobileSpec in tests.xml with comment

- Add CordovaMobileSpec in tests.xml, but comment it, and update README for declear
- Update CordovaMobileSpec test description
- Separate cordova samples in samples-cordova