Improve Event Page Action button logic

[MJDeligan]

There's a few states that aren't correctly handled on the event detail page.
Here's a chart to visualize all the states and the text the action button at the bottom should display:

https://excalidraw.com/#json=cW6aJa3rPdCWy6WxsfN3E,k1ST4rpiaqKVFMnQkPZgbw
(end nodes in green)

Click should be handled according to the actions.