Instant plugins reload

Changes include:
* all plugin reload logic gathered in one `loadOrConfigPlugin` fn,
* each plugin can now perform specific tasks just after its load `onChangeCb`,
* code DRY'ed,
* debug logs now show ticker source.
I wanted to define it verbatim, to show what can be expected here. 

Which brings me to a question, in `config.*.plugins.current` are two keys: `wallet` and `transfer`. `wallet` seems to make more sense here, but `transfer` is the one used to hold settings. Why is that? And why there's `wallet` then?