Investigate codecov.io test coverage report upload

[pwittchen]

In order to make build work after gradle update, I needed to switch to another jacoco android gradle plugin (old plugin didn't work with the new gradle version). It probably generates reports in another directory than original plugin and probably coverage reports are not uploaded. It need to be investigated.

Possible fix idea:

create new gradle task, which execute jacoco test report first and then, create appropriate dirs and copy report to the desired destination wanted by codecov.io. After that, update Travis CI config.

[pwittchen]

Reports from the recent builds after update were uploaded, so it was probably temporary error.