Assign Roles to Space from Spaces Management

[tsullivan]

Summary

Epic link: https://github.com/elastic/kibana-team/issues/785

This changes bring a new design to the management of Spaces in Stack Management / Security. We have a new page to view the details of the Space, and new UX to assign Roles to a Space.

Release Note

Added several UX improvements to the management of Spaces in Stack Management > Spaces, including the ability to assign Roles to an existing Space.

Checklist

Delete any items that are not applicable to this PR.

• [x] Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• [x] Unit or functional tests were updated or added to match the most common scenarios
• [x] Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• [x] Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• [x] This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• [x] This was checked for cross-browser compatibility