Explorer 2D for phones and tablets

[emalafeew]

Thanks again Auld. The ways in which I should be able to tell when the app is low on memory range from not working to fiddley. I picked the best one and tuned it to work on our Pixel phone and Samsung tablet, but think we have an S8 here to see why that doesn’t work. Hopefully will find a surer way. We’re focusing on other improvements for Play and Explorer so might not get back to this until next week