Add "copy url" per double click / click in network panel

Follow up for https://github.com/devtools-html/perf.html/pull/1456#discussion_r233557510

This PR contained a function to copy the URL of a network marker per double click on a row in the network panel.

Dumping the code here, so it might be useful.

```
import copy from 'copy-to-clipboard';

// copy URI
_onDoubleClick = (_event: SyntheticEvent<>): void => {
// strip marker name to url
const uri = this._cropNameToUrl(this.props.marker.name);
// copy url to clipboard
copy(uri);
};