Make Tabs a controlled component

[interactivellama]

• Make Tabs a controlled component (require parent to choose current tab by prop).
• Update to current SLDS markup Tabs - Clicking a Tab should allow the user to start using keyboard navigation #1053
• Remove DOM searches. Do not depend on DOM for state.
• Allow Popovers and tooltips on tabs. Allow popovers on tabs #1186

Props

• Add id to TabPanel and selectedId to Tabs.
• Removed Index related props (considering allowing in a hidden backwards compatible way)