Resolves #3950.

Unfortunately the design of scratch-storage doesn't make having multiple distinct POST urls easy at the moment. So for the time being, just make this request ourselves.

We are emitting targets update because the event is disabled in player mode, but gets re-enabled and re-emitted when switching back. The API on that function was changed to allow events to be marked "not project changes"

Adding relevant EV3/WeDo2 tutorial vid links, fixing up some json, removing some prop validation, etc.

Liked @paulkaplan’s suggestion that the property get renamed `showBranding` as we use ‘embedded’ in multiple ways that would get confusing.

The embedded project view is ‘playerOnly’, ‘fullscreen’ and ‘showBranding’.

use blue creating screen for new projects; revised alert text for copy, remix; saving messages don't dismiss alerts

Fixes 2 related issues:
1. The stage shrinking to 85% based on responsive stylings, which shouldn't happen when embedded in player only
2. When you click "small stage mode" in the editor then switch back to the project page view, it shouldn't show with small stage mode.