Introduce a logging system

[kelson42]

We have almost no log. Therefore, if someone complains about a bad behaviour of the app (for example, does not start at all), then we have no data to debug the case.

See #1320

[Ra7enV]

That's a great idea to indroduce a logging system for debug! And please let user to decide enable logging or not. For me, I don't like logs 'cuz it can expose some privacy.