[Feature] Add "Generate Thumbnail From Content" function to "Set Image" button.

[jeremymeyers]

Is your feature request related to a problem? Please describe.
There are currently two places to set a scene thumbnail.

1. The "Generate" menu at the scene menu

2. The "Set Image" button at the bottom

Adding "From current" to the lower image will reduce confusion, since the intended use of the button is to have a list of all the different ways to set the thumbnail.

Describe the solution you'd like
Add "From Current" to "set image" in "scene" view. Leave it in the context menu as well. Additionally, standardize language between the buttons. Are we calling it an "image" or a "thumbnail"

[0xb0af]

Maybe it would be even clearer to call it 'Snapshot' or 'Screenshot'? "Current" doesn't really mean much if you're not already aware of what the feature does.