- comment the display of image badge in the index.html cause 404 errors

The display of the project related image badge is deactivated because on the overview page
there is no project select and that results in an invalid badge url.
- update to the new karma threshold version 0.19

This version contains the applied fix to get the covergare with the onSpecComplete
method. See https://github.com/lithiumtech/karma-threshold-reporter/pull/3
- removed unused code that decarease ende2end test coverage
- added remove of maybe existing coverage folder created by instanbul

The instrumentation with istanbul create the folder public/js/bankapp/coverage
that contins the instrumented javascript files. This task instrument all
javascript files in the folder public/js/bankapp so ensure that before a
instrumention task is performed the output coverage folder not exists because
instanbul instrumented the already instrumented files in the coverage folder again.
To prevent that the output folder will be deleted before calling istanbul.