Add a prompt if the event is in draft status and the user publishes it

[amieiro]

If the event is in draft status and the user publishes it, she doesn't get a prompt.

This PR adds this prompt. To test it, you can test two different situations:

• Test 1:

  • Create a new event.
  • Click on the "Publish Event" button. You will get a prompt with the "Are you sure you want to publish this event?" text.
  • Update the content and click on the "Update Event" button.

• Test 2:

  • Create a new event.
  • Click on the "Save Draft" button.
  • Update the content and click on the "Update Draft" button.
  • Click on the "Publish Event" button. You will get a prompt with the "Are you sure you want to publish this event?" text.

Fixes #81.

[psrpinto]

Tested and it works