Implement the bulk of the new widget permission prompt design

Part 1 of https://github.com/vector-im/riot-web/issues/11262

This is all the visual changes - the actual wiring of the UI to the right places is for another PR (though this PR still works independently).

The help icon is known to be weird here - it's a bug in the svg we have. The tooltip also goes right instead of up because making the tooltip go up is not easy work for this PR - maybe a future one if we *really* want it to go up.

src/components/views/elements/TextWithTooltip.js

@@ -21,7 +21,8 @@ import sdk from '../../../index';
 export default class TextWithTooltip extends React.Component {
     static propTypes = {
         class: PropTypes.string,
-        tooltip: PropTypes.string.isRequired,
+        tooltipClass: PropTypes.string,
+        tooltip: PropTypes.node.isRequired,
     };
 
     constructor() {
@@ -49,6 +50,7 @@ export default class TextWithTooltip extends React.Component {
                 <Tooltip
                     label={this.props.tooltip}
                     visible={this.state.hover}
+                    tooltipClassName={this.props.tooltipClass}
                     className={"mx_TextWithTooltip_tooltip"} />
             </span>
         );