Fix: Update JSS plugin dependencies to fix peer dependencies warnings (…

…styleguidist#1470,  fixes styleguidist#1467)

New: Add --port command line option to change the dev server port (st…

…yleguidist#1460, fixes styleguidist#936)

New: Modifier to add whitespace between example components (styleguid…

…ist#1456, fixes styleguidist#841)

Let users to be able to add padding between example components without
adding manual styling to their example code. This adds the `padded` modifier option
to the Playground that adds padding between each example component in that block.

```jsx padded
<Button>Push Me</Button>
<Button>Click Me</Button>
<Button>Tap Me</Button>
```

Fix: Allow isolated components with duplicate names (fixes styleguidi…

…st#1454)

If you have more than one component with the same name, the isolated mode will incorrectly show all of the components of the same name (instead of just the one you clicked on).

This fix solves the issue by prepending the existing hash path from the page the user came from. By prepending this hash path, Styleguidist correctly scopes the isolated example to just the desired component.

Changelog: 🚀

Mostly code cleanup (use official React Context API, remove deprecated React APIs and patterns, etc.) and dependencies updates.

## Breaking changes

* Node 8.9 is the lowest supported version
* React 16.8 is the lowest supported version

Docs: Add a screenshot

Fix: Update react-dev-utils to ^9.0.3 (styleguidist#1422)

Fix: Don't show empty sidebar (styleguidist#1423)

Fix: Single sections can contain only sections (styleguidist#1414)

If a section contains only one subsection, Styleguidist will try to optimize. It will make the section disappear and show its components instead. If this section only contain sections, no components, it should optimize to sections and not to components.

Fix: Highlighting currently selected page on sidebar broken with sect…

…ions (styleguidist#1405)

Fixes styleguidist#1375