arrow

ARROW-3866: [Python] Column metadata is not transferred to tables in pyarrow

Use columns' existing metadata to create the new fields in `Table.from_arrays()`.
Also persists the original `nullable` value.

Happy to change things! Thank you for putting a newbie label on it.

Author: Tanya Schlusser <tanya@tickel.net>
Author: Krisztián Szűcs <szucs.krisztian@gmail.com>

Closes #3160 from tanyaschlusser/ARROW-3866 and squashes the following commits:

005940ea <Tanya Schlusser> Move the test for preserved metadata to a separate function. Add a test that nullable=False is preserved.
e4256a17 <Krisztián Szűcs> use column.field()
76216eae <Tanya Schlusser> Arrow-3866:  keep field matadata for columns passed to pa.Table.from_arrays()
33950a83 <Tanya Schlusser> ARROW-3866:  test to confirm column metadata is added when calling pa.Table.from_arrays(column_list)