Improve Performance

[sleidig]

Currently simply switching between different screens produces a noticable lag. We should look into performance issues to reduce that problem.

[sleidig]

In the current situation, we need a splash screen during the long startup phase: #59

[sleidig]

Displaying the autocomplete dropdown for task selection takes 2-3 seconds even with the new database cache. The MainTaskSuggestor also needs to cache its list until anything changes (or continually update it?)