Use hooks

We should use React hooks once they land in a stable release! Here are a couple first ideas:

• Rework theming system to be based on useContext to avoid DevTools bloat with ThemeConsumer components
• Implement useTheme hook (see #2340)
  • Maybe remove withTheme HOC in favor of the hook?
• Rework StyleSheet infrastructure to use hooks

Any other ideas for how we could leverage hooks?

[probablyup]

Something like:

const className = useStyle`
  color: ${p => p.theme.colors.red};
`;

Is that possible, using a TTL as a hook?

[sibelius]

is this enough to get theme?

import { useContext } from 'react';
import { ThemeContext } from 'styled-components';

export const useTheme = () => {
  const theme = useContext(ThemeContext);

  return theme;
};