Refactor Selector API and implement ComplexVisTypeSelector

[axelboc]

BREAKING

• I replace the optionComponent prop of Selector with a cleaner renderOption prop. This simplifies a few things, including removing the need for dedicated option components (ScaleOption and ColorMapOption).
• I replace the now-removed ColorMapOption, which was exported in the lib to address Customizing toolbar #1377, with a new component called ColorMapGradient that takes care only of rendering a little gradient preview for a given color map (which should in fact cover more customisation use cases).

NEW FEATURE

• I create a component called ComplexVisTypeSelector (in line with ColorMapSelector and ScaleSelector) to reduce duplication, and I export it in the lib;
• I move enum ComplexVisType to the shared package and I export it in the lib; I also replace its values and stop relying on them for display purposes (axis label, plot title, selector options), as this seemed very brittle and prevented displaying different labels in different places.