[META] 11.x feature updates

@anybody, regarding the scheduler integration: I'm still a bit unsure about how this could be achieved properly, as the simple plugin implementation does not seem to work yet. As we discussed, would you take a look?

Unfortunately, due to the structuring of the tracker settings, I believe it is simply not possible to set a default tracker:
The tracker settings themselves are in the "ad" module, while the local tracker is the "ad_track" module. This is that way because you are able to extend the module with custom trackers from other modules, which will then also appear in the select list.
So, we have three options here, all of which I don't find particularly good:

1. Place the tracker settings into the "ad_track" module (Caveat: Local tracker is always present even if unwanted)
2. Require the "ad_track" module to be enabled when installing "ad" (Caveat: same as above)
3. Overwrite the setting value when "ad_track" is installed afterward (Caveat: would disable any custom tracker already selected and delete the data!)

Another option would be to display a message after "ad" is installed: "You need to set a tracker in the settings in order for tracking impressions to work. If you don't have a custom tracker, you should enable ad_track" or something like that, but that would only be my last resort.

@anybody, what do you think of this?

@grevil this is ready so far, please review by time and autofix issues. I think we'll surely find some points for @lrwebks left to resolve next week.

And let's please close all fixed subissues then.