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ARROW-4139: [Python][Parquet] Wrap new parquet::LogicalType, cast min/max statistics based on LogicalType

This changes the behavior of `Statistics.min` and `Statistics.max` to return the decoded logical value, such as a UTF-8 string, uint64 value, timestamp, etc.  I added `min_raw` and `max_raw` attributes to return the raw physical type value

Also fixes ARROW-5166 (uint64 as int64 overflow)

I found the `isAdjustedToUTC` parameter for `TIME` logical type to be weird, so I'm changing the Arrow conversion layer to always set this so we can get the TIME_MILLIS / TIME_MICROS converted type to be set in those cases.

Author: Wes McKinney <wesm+git@apache.org>

Closes #4680 from wesm/ARROW-4139 and squashes the following commits:

11ced9e6c <Wes McKinney> Add utf-8 coding to test_parquet.py
54f974a53 <Wes McKinney> Follow changes in parquet::arrow unit tests
283b69aba <Wes McKinney> Write version 2.0 files
a67746e44 <Wes McKinney> Wrap new parquet::LogicalType, cast min/max statistics based on LogicalType in Python API