Clean up UI code and colors

[tomcl]

The time has come to revisit the UI - currently using Fulma CSS. That would have the big benefit maybe of removing the unpleasant large Bulma SCSS dependence.

Bulma is still the best bet for CSS - although there is now another option it is not obviously better.

Feliz-bulma is better maintained than Fulma and wraps Bulma using Feliz-style UI elements - which are generally easier to use.

Proposal

1. Add Feliz.Bulma and Feliz
2. Try and find a cleaner way to reference bulma than the current scss (look at how Feliz sites do this)
3. Revisit colors throughout the UI - move from white Issie to pleasant coloured Issie (but schematic editor maybe stays white)
4. (optional) Convert (bit-by-bit) current Fulma/react UI to equivalent Feliz.Bulma and Feliz (react) UI.
5. (optional) When finally complete, delete Fulma

Fulma and Feliz.Bulma can coexist and are basically equivalent - so converting Issie from Fulma to Bulma can be done gradually and fairly quickly.