Add timer for the complete map

[otacke]

As an author, I want to be able to set a time limit for the whole map.

As a user, when a time limit for the whole map is set, I want to (not really, but hey) be game over and taken to the end screen for losing.

• Needs to ensure that exercise timers are stopped.
• Needs to add a confirmation dialog with message.
• Needs to add an exception for when the end screen is shown.

[otacke]

Added in https://github.com/otacke/h5p-game-map/commit/667724dae6e216ea08675d3742f4014560c78e09