Allow admin to add new environments in the UI

[ablack3]

The administration section of the app has an environments tab. However it is not clear how an administrator can add a new environment. When I set up the application I do not see any environments and I need to be able to easily add new environments for new studies.

offline use case

For offline environments we need to provide docker images or tar.gz environments as files that will be transferred to the offline machine via USB drive. The admin would then need to upload a file (docker image or tar.gz) to Arachne datanode to add the new environment.

online use case

For online machines the admin should be able to provide the url for the docker image or tar.gz file through the datanode UI which will then be downloaded from the internet and added as a new runtime environment for Arachne.

Thanks!

[konstjar]

To review after v2.0.3 and to specify