Handle too long event names

[Joliv3r]

Currently if an event is created with a title of more than 50 characters and no defined slug Django will crash. This can be fixed by forcing the user to have shorter titles, by forcing them to create a shorter slug, or increasing the maximum length of the slug.

[Joliv3r]

For some reason this issue does not replicate locally, so my fix did not work.

[Joliv3r]

Fixed by #682 by limiting headline length.