feat: manipulate ConsoleLog events on app's side

[juniorklawa]

Hi!

I've added the possibility to handle ConsoleLog events on the app's side, not only on the library's side.

Imagine a scenario where I need to store console.log output on a variable for example, with the actual implementation I can't because the output of console.log events is only accessible on the library's side.

So this code:

Will have this output:

Because this is how flutter_js is dealing with console events:

With my implementation (setting useFlutterTerminal to false) is now possible to choose if you want the console events to be handled by the library or app side

Like this:

Giving this output:

I am not so sure if useFlutterTerminal is the best name for it, I am accepting suggestions @abner

Thanks!

[MulverineX]

This will be handled in an upcoming release of mercury, openwebf/mercury#24