[usecase-webapi] Add 'Clear Console Output' button for telephony

- Failure analysis: https://crosswalk-project.org/jira/browse/XWALK-2787
                    https://crosswalk-project.org/jira/browse/XWALK-2888
                    https://crosswalk-project.org/jira/browse/XWALK-2889

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Tizen IVI]
Unit test result summary: pass 0, fail 1, block 0