Classify closely related and versioned licenses

@pombredanne at https://github.com/nexB/scancode-toolkit/issues/2399

> There is a class of license notice that is problematic which are closely related and versioned licenses
>
> The licenses involved with this class of ambiguous detections are:
>
> mostly the A/L/GPL with and without versions
> to a lesser extent, other GFDL license
>
> The scan yields these licenses (scan has been edited for brevity):

```
"licenses": [
{
"key": "gpl-1.0-plus",
"score": 85.0,
"start_line": 1,
"end_line": 1,
"matched_text": "the gpl"
},
{
"key": "gpl-3.0-plus",
"score": 4.0,
"start_line": 2,
"end_line": 2,
"matched_text": "therefore [this] is licensed under [the] gpl"
},
{
"key": "gpl-2.0",
"score": 100.0,
"start_line": 2,
"end_line": 2,
"matched_text": "licensed under the gpl 2."
}
],
```

This should be a new class of detected license issue:- `closely-related-license-notices`

ToDo:

1. Add this class of issue
2. Add heuristic to classify these correctly