Display corruptions since upgrading to v2.15

Ok, just fixed this if you update all apps from the app loader.

@halemmerich it's an interesting idea about the widgets, but I think right now, changing the way widgets are defined and loaded is a bit too much of a wide-sweeping change - I'm pretty sure we'd create more bugs than we fixed :)

I was just about to add a default-off option for fast-loading in the launcher, and I realised that now .bootcde caches the clock's filename, the loading of the clock info is only done once when the clock changes. So instead what I've done is added clockHasWidgets to the settings, and this is updated either by the boot code or the settings menu when the clock changes.

So, this should fix it with no impact in speed (apart from maybe <0.5s when changing the clock)