Update to Julia 1.3.0

Modify the way to change user uid/gid

Updated Julia version number and checksum to have Julia 1.3.1 be installed instead of 1.2.0.

Updated the install commands for Julia to use version 1.3.1 instead of 1.2.0

Update ubuntu base image.

Twistlock vulnerability scanning showed OS issues removable by upgrading of package versions.

Configure Python Version with Build Arg

Add sudo recipe

upgrade to tensoflow2

Add maintainer help wanted

update jupyterlab to 1.2.1

fix typo

With JupyterLab 1.1, --dev-build=False is no longer necessary.

Make fix-permissions executable by all

Don't upgrade base image

Update Miniconda to 4.7.10 and conda to 4.7.12

Address updating base notebook to jupyterlab 1.1.3

Add link to sage-notebook Community Stack

Bump Julia to 1.2.0

Added sage-notebook as per https://github.com/jupyter/docker-stacks/blob/master/docs/contributing/stacks.md

Sort package installation lines alphabetically for easier comparison

typo correction on env variable: replacing $USER with $NB_USER since $USER is not set
test if group exists before trying to add a new group

Workaround of a Docker bad handling of sparse files
Fixes #923