Add story events

[otacke]

As an author, I want to be able to add story events based on rules.

A story event could be a combination of an image and some text, potentially also audio) that are combined in an overlay (cmp. SuperMarioWorld). The author could set up a story event and then define rules when this should appear. Rules could e.g. be based on:

• time left
• score achieved
• stage unlocked/opened/cleared
• number of stages completed/left
• potentially combinations of the above