Users want browser to open when Dash is ready

[anders-kiaer]

When running webviz build some_config.yaml, users want the webviz application to open automatically in default browser.

Consider doing the same when running webviz build some_config.yaml --portable ./some/outputfolder.

[anders-kiaer]

Relevant:

• https://docs.python.org/3.7/library/webbrowser.html
• https://stackoverflow.com/questions/30548758/how-do-i-know-that-the-flask-application-is-ready-to-process-the-requests-withou