added possibility show log messages in console commands

BC break: no
New feature: yes

Can be enabled with
```
monolog:
    handlers:
        console:
            type:  console
```

It's consistent with all the rest because you can use the existing `channels` option to just print some channels to the console. Also you can specify a custom formatter etc. So really flexible.

```
monolog:
    handlers:
        console:
            type:  console
            channels: custom
```

Todo:
- [x] use a custom handler that uses ConsoleOutput::getErrorOutput ('php://stderr') for errors
- [x] add tests
- [x] add a new default formatter for console handler that colors the output depending on log level
- [x] add configurability for the mapping of verbosity to minimum log level
- [x] maybe put `ConsoleHandler` and `ConsoleFormatter` into the MonologBridge instead?