Jupyter-enterprise-gateway

The Jupyter Enterprise Gateway 1.2.0 release provides some dependency updates and multiple bug fixes as listed below:
* Tolerance to Tornado 6.x
* Update to Jupyter Kernel Gateway 2.3.0
* Update to Apache Toree 0.3.0
* Update to Yarn Client API 0.3.3
* Tolerate errors when closing response sockets
* Properly use provided YARN RM port
* Reset watch-activity callback on remote-proxy restarts

This release incorporates the following commits:

- [Properly set PYTHONUSERBASE relative to user home folder](https://github.com/jupyter/enterprise_gateway/commit/c0b29607fdf231b4f4601937185e925f091c48c2)
- [Fix max-kernels-per-user when KERNEL_USERNAME not set](https://github.com/jupyter/enterprise_gateway/commit/a9d0364752ad7dbbf3b40311fbaf18507624c496)
- [Avoid use of backslash operator when working with JSON](https://github.com/jupyter/enterprise_gateway/commit/a396b0e0aa9c952fe910c11d9f98103fb58ad92d)

The Enterprise Gateway 1.1.0 release provides enhanced security support adding support for YARN endpoints protected by SPNEGO and other bug fixes as listed below:

* Add support to YARN endpoints protected by SPNEGO
* Allow enterprise gateway to ignore the SIGHUP signal
* Add the Enterprise Gateway version stamp to the startup message
* Update Scala and SBT dependencies to the latest version

Thanks tf3193 for helping out with the fix for SIGHUP.

The Enterprise Gateway 1.0.2 release provides minor bug fixes around incompatible changes on 3rd party dependencies.

* Use yarn-api-client release version below 0.3.0 to avoid issues with incompatible API changes.

- Fixes issue seen in Python 3 environments to detect launch failures (436)
- Adds optimization for using `DistributedProcessProxy` on local servers (430)

Thanks to ziedbouf for helping out with the python 3 issue.

Jupyter Enterprise Gateway 1.0.0 builds on its 0.9.4 release with various issue resolutions, but, more importantly, marks an important milestone for the project itself. With this release, Enterprise Gateway 1.0.0 officially supports Hadoop YARN and IBM Spectrum Conductor resource managers, enabling remote kernel distribution across a managed cluster by leveraging its pluggable _process proxy_ framework. In addition, general ssh-based distribution can be accomplished via the `DistributedProcessProxy` plugin.

Here are some of the additions since our 0.9.4 release:
- Code coverage monitoring 415
- Bundle Toree assembly jar into Kernelspec distro 411
- Update Apache Toree dependencies to Release 0.2.0-incubating 412
- Update JKG dependency to 2.1.0 release 410
- Detect launch failures prior to timeout 404
- Update java build in yarn-spark image 391
- Update project readme file 388
- UTF-8 decode stdout from curl subprocess in YarnClusterProcessProxy 379

Thank you to the following contributors since 0.9.4:
- Alan Chin (akchinSTC)
- Andrew Otto (ottomata)
- Kevin Bates (kevin-bates)
- Luciano Resende (lresende)