Update `pd_utils.get_wide_mask()` to select just index or column values

[BenTaylor-TfN]

Update pd_utils.get_wide_mask() to allow the selection of data based on just the index_select or col_select arguments. For example, the function currently works like:

    >>> get_wide_mask(df,col_select=[0, 1],index_select=[1, 2, 3])
    array([[False, False, False, False],
           [ True,  True, False, False],
           [ True,  True, False, False],
           [ True,  True, False, False]])

We'd like the function to work like:

    >>> get_wide_mask(df,col_select=[0, 1])
    array([[ True,  True, False, False],
           [ True,  True, False, False],
           [ True,  True, False, False],
           [ True,  True, False, False]])

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