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ARROW-1744: [Plasma] Provide TensorFlow operator to transfer Tensors between Plasma and TensorFlow

This is based off of #2046 from @pcmoritz and @concretevitamin, who wrote the original TensorFlow Op with help from @ericl.

In addition to the previous PR, this supports serialization of arbitrary type tensors.

To get it working, arrow has to be compiled in the following way:

```
cmake -DARROW_PLASMA=on -DARROW_TENSORFLOW=on -DARROW_PYTHON=on ..
make -j8
sudo make install
```

And pyarrow like that:

```
PYARROW_WITH_PLASMA=1 PYARROW_WITH_TENSORFLOW=1 python setup.py develop
```

The PR also includes utilities that should be generally useful in converting between TensorFlow and Arrow. It is currently supposed to be used to transfer weights in and out of TensorFlow but hopefully in the future there will also be support for data Tensors.

Author: Philipp Moritz <pcmoritz@gmail.com>
Author: Peter Schafhalter <pschafhalter@berkeley.edu>

Closes #2104 from pschafhalter/tensor-serialization and squashes the following commits:

50c6635 <Philipp Moritz> don't import tensorflow on manylinux1
3b7bbc7 <Philipp Moritz> skip tests that use tensorflow inside of manylinux1 container
097d48d <Philipp Moritz> Merge branch 'master' into tensor-serialization
df44982 <Philipp Moritz> Merge branch 'master' into tensor-serialization
13e4db3 <Philipp Moritz> remove setting the deleted variable to nullptr
b79c710 <Philipp Moritz> more fixes
200ad89 <Philipp Moritz> move build flags earlier
b4b4134 <Philipp Moritz> tensorflow namespace
b0731ad <Philipp Moritz> fixes
10e369a <Philipp Moritz> more fixes
01e580c <Philipp Moritz> more cleanups
027d683 <Philipp Moritz> fix
e494f28 <Philipp Moritz> clean up code
1ef52d0 <Philipp Moritz> fix
90757c1 <Philipp Moritz> fix gpu code
d5d3740 <Philipp Moritz> fix
d137fcf <Philipp Moritz> compile pyarrow without cxx-11 ABI too
81f34ff <Philipp Moritz> fix
b4e02e1 <Philipp Moritz> fix test
749e21e <Philipp Moritz> cleanups and test
fb8786e <Philipp Moritz> fix
bc3a5bb <Philipp Moritz> cleanups
56c9cf1 <Philipp Moritz> fix
c6066ab <Philipp Moritz> fix
2fe3523 <Philipp Moritz> cleanups
4dc4ff3 <Philipp Moritz> fix TensorFlow test
3264efe <Philipp Moritz> test
acc1f0b <Philipp Moritz> fix test
372551f <Philipp Moritz> pkg-config
64ee050 <Philipp Moritz> fix test
d83b9ae <Philipp Moritz> fix test
2385e7c <Philipp Moritz> fix
af4eb2f <Philipp Moritz> cleanups
6a34556 <Philipp Moritz> move things around
afa5dba <Philipp Moritz> fix
b29bf39 <Philipp Moritz> linting
14c9e50 <Philipp Moritz> fix linting
eb1a576 <Philipp Moritz> fix
47a21c9 <Philipp Moritz> add license
1c8c5fa <Philipp Moritz> Merge branch 'master' into tensor-serialization
1442be0 <Philipp Moritz> test more dtypes
ead1a2e <Philipp Moritz> test
af68371 <Philipp Moritz> debug2
a2131ad <Philipp Moritz> debug
531f4a7 <Philipp Moritz> fix
be83a20 <Philipp Moritz> try datatype
077266b <Philipp Moritz> fixes
1164d5a <Philipp Moritz> fixes
4f641c3 <Philipp Moritz> fix warnings
a674720 <Philipp Moritz> fix
140a2b9 <Philipp Moritz> needs debugging
8b1dd8c <Philipp Moritz> get write path working
d7ead2b <Philipp Moritz> fix
d291f64 <Philipp Moritz> fix
f461b38 <Philipp Moritz> fix linting
3b01abe <Philipp Moritz> fix
232ed6f <Philipp Moritz> add tensor utilities
f7466de <Peter Schafhalter> Formatting
3ed436b <Peter Schafhalter> Formatting
f4ad8e5 <Peter Schafhalter> Check that all tensors have the same dtype
f601bb0 <Peter Schafhalter> Convert Tensor type to Arrow
4167d1d <Peter Schafhalter> Fix tensor serialization
e261f2c <Philipp Moritz> fixes for the op
d381ff3 <Philipp Moritz> fixes
c705d53 <Philipp Moritz> fix for python 2.7
22b5564 <Philipp Moritz> fix wheel building
ae2e7ca <Philipp Moritz> adapt code for arrow
f6cef78 <Philipp Moritz> add initial tensorflow op