[WIP] Testing with Travis

[patrickjahns]

WIP to have this app tested on travis

Tasks

• check how to inject credentials for tests
• check if we can limit concurrency to 1 (so individual jobs would not create cross-talk issues) or find a way to have individual credentials per build job
• fix failing tests - also see: Failing dropbox unit tests core#19868

[PVince81]

This will likely not be possible as we need oauth creds from Dropbox and also make sure to not overload / reach API quota with too many builds. And said oauth creds will need to be refreshed within the refresh token timeline.

[patrickjahns]

Let's close this for now - would need to be move to drone anyway