Fix colors and logo link

Cleanup and add a bit to the pages

Link yo JupyterBook

Drop a few more non-runnable files

Probfit included

Fix occasional exception when loading data

Adding iMinuit

Drop file with ipybind

Drop a file with CuPy from runnable status

Longer timeout on CI

Matplotlib 3.2.0 doesn't like SymPy

Adding GH workflow

Some files now use Black

Cleanup, make mostly runnable

Fix recording links, notes on contributing