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

[ameshkov]

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.