Add ViewUser component

[bfbachmann]

You'll need to create a new component called ViewUser.js.
See https://reactjs.org/tutorial/tutorial.html for a tutorial.

[bfbachmann]

You'll need to update App.js by adding a route that allows you to get to the ViewUser component:

<Route path='/users/:username' component={this.getViewUserPage} />

You'll also have to add a getViewUserPage method to App.js that returns a ViewUser component that is initialized with the user's username:

getViewUserPage(filter) {
        const username = decodeURIComponent(filter.match.params.username);
        return <ViewUser
            client={this.props.client}
            username={username}
        />;
    }