some VPN apps are broken on Android 7.1 (and below?)

fixes #4058

fixes #4057

fixes #4053

fixes #4049

people with half a brain will implicitly follow those guidelines any way and
provide the information requested in the issue template.

The vast majority of people have ignored the issue template in the past anyway.

Thank you to @ailicic for figuring out the new API.

Closes #4050

Upon accepting a video call on a device that can not establish a video track on
its own (for example by not having a camera), displaying the video enable/disable
button would fail. This commit defaults this button to disabled.