Nightingale structure - AlphaFold colouring

[aurel-l]

Describe the bug
When loading an AlphaFold predicted structure, the structure is not coloured using the usual AlphaFold colouring for model confidence

To Reproduce
Load any AlphaFold prediction

Expected behavior
Should be displaying same colours as on the AlphaFoldDB website (see screenshot below)

Screenshots

[aurel-l]

Note that the goal of the structure viewer is to use the smallest possible amount of code from the Molstar library as to reduce its footprint. We should avoid using the UIPlugin loading everything.

We need to extract what bit of code is responsible of the colouring and just add this and nothing more.