mark2 configuration with a single attribute

This moves mark2 configuration to a single top-level attribute:

```
node['minecraft]['mark2']['properties']
```

It works, but I'm not sure how intuitive will be so I'll leave that up to
you. With this PR configuration would look like:

```node['minecraft]['mark2']['properties']['java']['cli.X.ms'] ='1024MB'```

or

```
node['minecraft]['mark2']['properties'] = {
    "java" => {
        "cli.X.ms" => "1024MB",
        "cli.X.mm" => "1024MB"
    },
    "mark2" => {
        "jar-path" => "*.jar",
        "shutdown-timeout" => "60"
    },
    "plugin" => {
        "log.enabled" => "true",
        "log.gzip" => "false",
    }
}
```

but it seems like it might(?) be better to serialize the attribute object
completely so that it could instead be like:

```
node['minecraft]['mark2']['properties']['java']['cli']['X']['ms']='1024MB'
node['minecraft]['mark2']['properties']['mark2']['jar-path] = "*.jar"
node['minecraft]['mark2']['properties']['mark2']['shutdown-timeout] = "60"
node['minecraft]['mark2']['properties']['plugin']['log']['enabled'] = "true"
node['minecraft]['mark2']['properties']['plugin']['log]['gzip'] = "false"
```

I'm fine with either really, what do you think?