Comment 27 for bug 1462489

This will be implemented by added a new policy group, 'keep-display-on' that apps can start using. As such, app policy will not have to be regenerated on OTA upgrade for this change (since no apps are using this new policy group). This requires updating the review tools due to comment #25 (trust prompt won't be implemented at this time, so limit the use of this policy group to only apps specifying the ubuntu-sdk or ubuntu-webapp templates). The addition of the policy group also requires a documentation change.