Bring API usages in line with the requirements of Android 10 (SDK 29)

Android Q (or 10 or 29 depending on your context) is here, and I want us to keep up rather than catch up.

Several API usage models are going away, and I think it's causing buggy-looking behavior on my Samsung device (though not yet on a Nexus tablet). When I run a Lint report:

* 'getExternalStorageDirectory()' is deprecated
* 'insertImage(android.content.ContentResolver, java.lang.String, java.lang.String, java.lang.String)' is deprecated
* 'getBitmap(android.content.ContentResolver, android.net.Uri)' is deprecated

This matches some GIYF investigations on the same topic. Android 10 appears to be taking additional steps to secure user privacy, and one consequence is that we're going to have to fix the way we handle media and external storage.

I'll iterate on this over the next few weeks.