Add onClick event functionality

[vwinstea]

In order to get from the homepage to the signup page, a user will need to click on an event on the calendar and then be taken to the signup page where the event will be displayed. In this task you will:

• Change the event click so it stores the event that was clicked on in the selectedEvent state.
• Pass this selected event to the sign up page. Note that this may require lifting state to App.tsx so the selectedEvent can be passed through a route, although you may also be able to use route params instead.