Replace "verbose" flag with an option to supply custom Logger implementation

Currently, the scriptlets library allows supplying a `verbose` flag that controls whether the scriptlet should write verbose output to the console.

I suggest replacing that flag with the ability to supply custom `Logger` implementation and encapsulate this logic inside.
Something simple like that:

```
interface Logger {
debug()
info()
error()
}
```

This will also require changing the CoreLibs and the extensions content script accordingly.