Block: Move tabIndex to wrapper component

See: #2934
See: https://codepen.io/aduth/pen/MQxRME

Something needs to capture the focus event, which is skipped by button press on the block's toolbar, but bubbles up wrongly to the parent's edit wrapper (which has tabIndex) and causes parent block to select itself.

components/toolbar/index.js

@@ -31,7 +31,6 @@ function Toolbar( { controls = [], children, className } ) {
 					<div
 						key={ [ setIndex, controlIndex ].join() }
 						className={ setIndex > 0 && controlIndex === 0 ? 'has-left-divider' : null }
-						tabIndex={ -1 }
 					>
 						<IconButton
 							icon={ control.icon }

editor/components/block-list/block.js

@@ -579,6 +579,7 @@ export class BlockListBlock extends Component {
 				data-type={ block.name }
 				onTouchStart={ this.onTouchStart }
 				onClick={ this.onClick }
+				tabIndex="0"
 				childHandledEvents={ [
 					'onKeyPress',
 					'onDragStart',
@@ -619,7 +620,6 @@ export class BlockListBlock extends Component {
 					onKeyDown={ this.onKeyDown }
 					onFocus={ this.onFocus }
 					className={ BlockListBlock.className }
-					tabIndex="0"
 					aria-label={ blockLabel }
 					data-block={ block.uid }
 				>