Redesign DataFrame structure

[akharche]

Extension for #801

• Implementation of new DataFrame structure based on lists instead of tuples
• Improved df.count() codegen for testing

Example:

df = pd.DataFrame({'A': [1,2,3], 'B': [.5, .6, .7], 'C': [4, 5, 6], 'D': ['a', 'b', 'c']})

(['A', 'B', 'C', 'D'],)
([array([1, 2, 3], dtype=int64), array([4, 5, 6], dtype=int64)], [array([0.5, 0.6, 0.7])], [array(['a', 'b', 'c'], dtype=object)])

Reproduce:

@njit
def run_df():
    df = pd.DataFrame({'A': [1,2,3], 'B': [.5, .6, .7], 'C': [4, 5, 6], 'D': ['a', 'b', 'c']})

    print(df._columns)
    print(df._data)

    return df.count()

[akharche]

Duplicate of #817