Fail with error instead of crashing

[JohanForngren]

If I mistype something, I would like the game to try to continue and instead giving we a warning or error in the console.

Examples:

- dude says: Hello
- dudesays: It's me
- dude says: Just wanted to say hi

Suggested message: "Warning: Action dudesays does not exist at Story.yaml:

- show exhibitA: AT LEFT
- show typo: AT CENTER
- show exhibitC: AT RIGHT

Suggested message: "Warning: Asset typo does not exist at Story.yaml:

[lunafromthemoon]

One way to do this:
Catch exception when parsing/executing task, if it fails, print the error. Specific error messages could be done per task eventually.
Currently you can also use debugMode: true (in config object in boot.js) to see step by step the execution of the story tasks.