Install tini from conda-forge

Change XDG_CACHE_HOME when using NB_USER

Switches to getting `tini` from `conda-forge`.

Update version of seaborn to 0.9.X

Adds config file initialization and updates Apache Mirror due to timeout issue

Adds the initial creation of the configuration file
jupyter_notebook_config.json to the image. This file
was missing as reported in issue #639 and caused an
error when trying to set a new password via the Web
interface.

Bumps the version of Jupyter Notebook to 5.6

Updates Apache Mirror URL because the current causes build timeouts

The mirror used now (mirrors.ukfast.co.uk) is fast enough and does not
point to an ad site and is already used in a different Dockerfile within
this repository.

[ci skip] Remove dead files w/ old versions

Fixed README, Jupyter Lab launch sample command

Fix #492: NB_GID adds a supplemental group, leaves primary untouched

Fix typo - Juptyer

Bumping up Spark and Conda to the current version

But stick with the same major and minor as the base miniconda installer

bump some packages

Updated recipe for pip and added conda example.

Updated the recipe for pip to include requirements.txt file.
Also included example for using conda to install packages.

- notebook 5.5
- matplotlib 2.2
- pandas 0.23
- scipy 1.1
- scikit-image 0.14
- statsmodels 0.9

Lock down ability to run su command.

Remove writable group file due to issues with being able to give su access when shouldn't be allowed.

Community stacks documentation

upgrade tini to latest version 0.18.0

upgrade tini to latest version 0.18.0 and also added the option to send signal to all child group processes as mentioned in docs

https://github.com/krallin/tini#process-group-killing