Rename to plasma

[Jeremy Tuloup]

To keep it consistent between:

• this repository
• the TLJH plugin
• the documentation
• the twitter account

We can rename and use the name "plasma" to refer to the project itself, instead of "plasmabio":

• the repo becomes: https://github.com/plasmabio/plasma
• the TLJH plugin becomes: tljh-plasma
• mentions to "PlasmaBio" in the docs become: "Plasma" (or "PLASMA"?)
• rename in LICENSE:

  plasma/LICENSE

  Line 3 in b1c8e6d

   Copyright (c) 2020, PlasmaBio Contributors 

• update README in https://github.com/plasmabio/tljh-repo2docker: plasmabio/tljh-repo2docker#17
• update readthedocs to https://plasma.readthedocs.io

[Pierre Poulain]

mentions to "PlasmaBio" in the docs become: "Plasma" (or "PLASMA"?)

I would say "Plasma"