Allow showcase for other frameworks and platforms.

Update button colors, as well as cursor for menumultiselect.

Use old tests for components.

Provide more tests for choice components.

Add tests for choice elements.

Start migrating tests, tsdoc across components.

Manage props directly and fix some linting errors across all categories.

Extract all components from showcase to their own packages.

Define all categories presently implemented.

Start separating trivial components to their own categories outside the
kitchen sink package.