Studio: backgrounds dropped during the game are picked up by the Resources button

Layer gets backgrounds/; StudioBackgrounds re-reads the file list and the background
cache and shows the current background (with _depth/_albedo) anew. The Resources
button sits on the transport bar (every tab); a new scene picks its background from
a list with the source mod. studio_live covers drop, reload, replace and export.

locale/en.properties

@@ -156,3 +156,12 @@ studio/log_text_checkpoint_restored = back to the checkpoint in {0}
 studio/drag_next_line = Drag to another line to run it next
 studio/next_line_failed = The dialog cannot continue from this line
 studio/log_text_next_line = next line moved to {0}
+studio/reload_assets = Resources
+studio/reload_assets_tip = Re-read backgrounds dropped during the game into backgrounds/ of a mod or of the layer ({0})
+studio/map_assets_hint = Put new backgrounds into backgrounds/ of your mod or of the layer ({0}), then press "Resources" on the bar above. A <background>_depth next to it feeds the lighting.
+studio/assets_reloaded = Resources re-read: {0} backgrounds, nothing new
+studio/assets_reloaded_new = Resources re-read: {0} backgrounds, new: {1}
+studio/log_text_assets_reloaded = resources re-read: {0} backgrounds, {1} new
+studio/background_current = Backgrounds of the current scene
+studio/backgrounds = Backgrounds
+studio/background_item = background {0} · {1}