Replace Promise with async/await

[tomholub]

continuation of #290

similarly how was done in #400 and #590

possibly after #402

It should not be one big PR. When possible, it would be better to make several PRs to change the app chunk by chunk. That way errors are less likely to slip in during refactoring, and also to prevent merge conflicts.

[tomholub]

This may take more than one PR to do comfortably. Just take a chunk of functionality and convert from Promise to Future like you have just done, then do another chunk, etc until the Promise library can be dropped from dependencies. Thanks!

[tomholub]

closed wrongly