Stability improvements

A lot of work has been done the last few weeks, but you might not have noticed. Most time has been spent reducing complexity, which is always a good thing. Quite some code was shared between the GUI, the public website and the API. Also, test code was running from a different directory instead of from a different url, making it necessary to have some nasty config checks in the main code.

That has all changed now. The source code has been refactored and now all parts have proper separation. On top off that ShadowTrackr now uses a Continuous Integration pipeline: on every code check-in we run automated sanity checks and tests.