Support for Python3

[zgbjgg]

Support for python 3 since python 2.7 lifecycle is ending.

In order to support PY3 we need this changes:

• All atoms now will be used as binaries since mapping data types is translated to bytes() and atoms are limited to 255 chars.
• Check a new decoder to change bytes() to str() from python side
• Allow worker start with py3, py2 or custom py path
• Fix tests to work with new implementation
• New version of JUN will be published as 0.2.0
• Support to manage engines: pandas or koalas, since migrating to py3 we are able to use koalas as engine to improve performance of JUN tasks.

If new tasks appears in the process of update the repo it will be added here. All work done in this release should be put in py3 branch.

[zgbjgg]

• Allow travis upgrade to run over py3 and fix pip commands

[zgbjgg]

For now the tests are working, only extend it's not working, we'll check ASAP.

[zgbjgg]

Environment in TRAVIS is now working, we are checking the issues with tests, 2 of them are related to credentials used to auth into plotly, so maybe these tests will be disabled. Keep in mind the extend tests is not working, checking any solution ASAP

[zgbjgg]

Extend is working now using add_trace 👌

[zgbjgg]

All is working and all tests are passing now into Travis! 😄 🎉