* Add onboarding plugin installation (step 2)
* Handle PR Feedback: Fix vertical label display on mobile, fix Jetpack connect URL generation, so we make sure the plugin is active first, add new constant for local calypso development, fix typo, refactor activatePlugin/installPlugin on the JS side, sanitize plugin name input.
* Add a vertical mode to the stepper component, and make some adjustments to the font weights.
Also adds a 'isPending' parameter to show a spinner for the currently active step.
* Handle PR feedback: Fix typo, add some margin to stop bouncing around in horizontal mode, add vertical example to devdocs.
* Fix linter errors