Automated wheel creation with cmake and more

[yxlao]

Usage

make                   # our regular make, creates build/lib/Python/open3d.so
make install           # does not install any python module
make python-package    # creates python package in build/lib/python_package
make pip-wheel         # creates wheel in build/lib/python_package/dist
make install-pip-wheel # installs wheel in virtualenv
make all-pip-wheels    # creates all wheels in PyPI: "open3d-python, py3d, ..."

Motivation

1. Later we'll have a mix of pure python code (e.g. python visulization) and
   compiled python module. The current installation mechanism only work with one
   compiled python module. Using approach in this PR, all python package files
   will first be grouped in to a wheel file, then installed.
2. Currently, make install installs the python module in the global user site.
   Therefore, it doesn't work with pip nor conda virtualenv.
   (see this discord discussion)
3. Currently creating pip wheels and especially releaseing pip wheels under
   different names is a painful manual process.
4. Currently we're including all python versions and all platforms inside a
   single wheel package. This is a simpler approach when we are doing the pip
   packaging manually, however the wheel size is large. With the automated
   process, creating wheels containing single compiled module is simple. Now
   the wheel size is about 12X smaller.
5. There are also some user feedback (e.g. Please allow to build just a python module #566) to separate python build and
   installation process.

---

This change is 

[syncle]

Reviewed 27 of 27 files at r1.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @yxlao, @takanokage, and @qianyizh)

---

src/Python/CMakeLists.txt, line 25 at r1 (raw file):

# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
# IN THE SOFTWARE.
# ----------------------------------------------------------------------------

I think we are not putting the license header in CMakeLists.txt

---

src/Python/CMakeLists.txt, line 34 at r1 (raw file):

    find_program(PYTHON_IN_PATH "python")
    set(PYTHON_EXECUTABLE ${PYTHON_IN_PATH})
endif()

This is great. This will resolve many python version conflicts (compiled with system Python but the output module is called with virtualenv Python) we had encountered. Just quick question. Why this lines are inside if (NOT PYTHON_EXECUTABLE) ? Can you explain bit more?

---

src/Python/install_pip_wheel.cmake, line 26 at r1 (raw file):

# IN THE SOFTWARE.
# ----------------------------------------------------------------------------

Dropping license header?

---

src/Python/Package/setup.py.in, line 30 at r1 (raw file):

setup(
    author='IntelVCL',

Open3D team?

[yxlao]

Reviewable status: 22 of 27 files reviewed, 5 unresolved discussions (waiting on @syncle, @yxlao, @takanokage, and @qianyizh)

---

src/Python/CMakeLists.txt, line 22 at r1 (raw file):

PYTHON_EXECUTABLE

---

src/Python/CMakeLists.txt, line 25 at r1 (raw file):

Previously, syncle (Jaesik Park) wrote…

I think we are not putting the license header in CMakeLists.txt

Done.

---

src/Python/CMakeLists.txt, line 34 at r1 (raw file):

if (NOT PYTHON_EXECUTABLE)
if (NOT PYTHON_EXECUTABLE) is when the user didn't specify the -DPYTHON_EXECUTABLE. In this case, we use the python executable in the current path.
Added comments in the code as well.

---

src/Python/install_pip_wheel.cmake, line 26 at r1 (raw file):

Previously, syncle (Jaesik Park) wrote…

Dropping license header?

Done.

---

src/Python/Package/setup.py.in, line 30 at r1 (raw file):

Previously, syncle (Jaesik Park) wrote…

Open3D team?

Done.