New check which find duplicate except clauses

flake8-bugbear already find duplicate exeptions in the same tuple, but across different except's this is not done

**Examples**:
```python
try:
    pass
except ValueError:
    pass
except ValueError:
    pass
```
```python
try:
    pass
except (ValueError, TypeError):
    pass
except (ValueError, UnicodeError):
    pass
```

I'm happy tp contribute this check 😄 