Add test for dockerized app

Test that dockerized app in travis runs without any console errors.
This would ensure that e.g. input files are loaded from `webviz_storage` and not local files.

Start by inspecting the Travis configuration and Docker setup for webviz-subsurface, then run the dockerized app in the same CI context. The test should verify that the app completes without console errors and that input files are loaded from webviz_storage rather than local files.

Written by the indexing model from the issue text.