Add level argument to filter (?) 
Assume we have a DataFrame that looks something as follows and we want to *exclude* the column for "Total" in the second level of the column:

```python
In [2]: mi = pd.MultiIndex.from_product([['2018'], ['Q1', 'Q2', 'Q3', 'Q4', 'Tot
   ...: al']])                                                                  

In [3]: df = pd.DataFrame([[1, 2, 3, 4, 10]], columns=mi)                       

In [4]: df                                                                      
Out[4]: 
  2018               
    Q1 Q2 Q3 Q4 Total
0    1  2  3  4    10
```

There is not an easy way to do that. One option is to add the `level` argument to `DataFrame.filter`, though there are ongoing discussions around if we want to keep or deprecate that method.