Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- `README.md`:
  Our README.md files are completely different. Discarded upstream changes.
- `app/javascript/core/admin.js`:
  Updating rails-ujs, no real conflict, but a comment to close to changed
  code. Various glitch-soc-only files have been updated to match those changes,
  though.
- `package.json`:
  No real conflict, just an additional dependency in glitch-soc that was too
  close to something updated upstream. Took upstream's changes.

config/routes.rb

@@ -346,7 +346,7 @@ Rails.application.routes.draw do
         end
       end
 
-      resources :media,        only: [:create, :update]
+      resources :media,        only: [:create, :update, :show]
       resources :blocks,       only: [:index]
       resources :mutes,        only: [:index] do
         collection do
@@ -463,6 +463,7 @@ Rails.application.routes.draw do
     end
 
     namespace :v2 do
+      resources :media, only: [:create]
       get '/search', to: 'search#index', as: :search
     end