ARROW-1408: [C++] IPC public API cleanup, refactoring. Add SerializeSchema, ReadSchema public APIs

[wesm]

This is mostly moving code around. In reviewing I recommend focusing on the public headers. There were a number of places where it is more consistent to use naked pointers versus shared_ptr. Also some constructors were returning shared_ptr to subclass, where it would be simpler for clients to return a pointer to base.

This includes ARROW-1376 and ARROW-1406

[wesm]

Summary of deprecations:

• Deprecated in favor of an InputStream based version (since the only difference is a Seek)

ARROW_EXPORT
Status ReadRecordBatch(const std::shared_ptr<Schema>& schema, int64_t offset,
                       io::RandomAccessFile* stream, std::shared_ptr<RecordBatch>* out);

• RecordBatchStreamWriter and file writer return std::shared_ptr<RecordBatchWriter> since they have identical APIs

[cpcloud]

+1 LGTM. The API looks much more unified this way.

[cpcloud]

Looks like a transient conda error on appveyor:

CondaHTTPError: HTTP 502 BAD GATEWAY for url <https://repo.continuum.io/pkgs/pro/win-64/repodata.json.bz2>

[wesm]

Alright, merging