Merge branch 'plain-bg' into 'develop'

Solid color wallpaper support

See merge request pleroma/pleroma-fe!1314

src/i18n/en.json

@@ -329,6 +329,7 @@
     "hide_muted_posts": "Hide posts of muted users",
     "max_thumbnails": "Maximum amount of thumbnails per post",
     "hide_isp": "Hide instance-specific panel",
+    "hide_wallpaper": "Hide instance wallpaper",
     "preload_images": "Preload images",
     "use_one_click_nsfw": "Open NSFW attachments with just one click",
     "hide_post_stats": "Hide post statistics (e.g. the number of favorites)",
@@ -516,6 +517,7 @@
         "inputs": "Input fields",
         "faint_text": "Faded text",
         "underlay": "Underlay",
+        "wallpaper": "Wallpaper",
         "poll": "Poll graph",
         "icons": "Icons",
         "highlight": "Highlighted elements",