Support for unnamed grouping

Grouping in class diagrams without names is now supported.

@startuml
package {
}
// note: unnamed namespaces are not supported in platuml.
namespace {
}
node {
}
folder {
}
frame {
}
cloud {
}
database {
}
rectangle {
}
@enduml

[
  {
    "elements": [
      {
        "name": "",
        "title": "",
        "type": "package",
        "elements": []
      },
      {
        "name": "",
        "title": "",
        "type": "namespace",
        "elements": []
      },
      {
        "name": "",
        "title": "",
        "type": "node",
        "elements": []
      },
      {
        "name": "",
        "title": "",
        "type": "folder",
        "elements": []
      },
      {
        "name": "",
        "title": "",
        "type": "frame",
        "elements": []
      },
      {
        "name": "",
        "title": "",
        "type": "cloud",
        "elements": []
      },
      {
        "name": "",
        "title": "",
        "type": "database",
        "elements": []
      },
      {
        "name": "",
        "title": "",
        "type": "rectangle",
        "elements": []
      }
    ]
  }
]

Furthermore we now support newlines before blocks in class diagrams

@startuml

package P1
{
}

class C1
{
}

interface I1
{
}

enum E1
{
}
@enduml

[
  {
    "elements": [
      {
        "name": "P1",
        "title": "P1",
        "type": "package",
        "elements": []
      },
      {
        "name": "C1",
        "title": "C1",
        "isAbstract": false,
        "members": [],
        "extends_": [],
        "implements_": [],
        "generics": [],
        "stereotypes": []
      },
      {
        "name": "I1",
        "title": "I1",
        "members": [],
        "extends_": [],
        "implements_": [],
        "generics": [],
        "stereotypes": []
      },
      {
        "name": "E1",
        "title": "E1",
        "members": [],
        "extends_": [],
        "implements_": [],
        "generics": [],
        "stereotypes": []
      }
    ]
  }
]