Import feature for following/blocking lists (addresses #62, #177, #201, #454)

config/locales/en.yml

@@ -85,6 +85,13 @@ en:
     validation_errors:
       one: Something isn't quite right yet! Please review the error below
       other: Something isn't quite right yet! Please review %{count} errors below
+  imports:
+    preface: You can import certain data like all the people you are following or blocking into your account on this instance, from files created by an export on another instance.
+    success: Your data was successfully uploaded and will now be processed in due time
+    types:
+      blocking: Blocking list
+      following: Following list
+    upload: Upload
   landing_strip_html: <strong>%{name}</strong> is a user on <strong>%{domain}</strong>. You can follow them or interact with them if you have an account anywhere in the fediverse. If you don't, you can <a href="%{sign_up_path}">sign up here</a>.
   notification_mailer:
     digest:
@@ -124,6 +131,7 @@ en:
     back: Back to Mastodon
     edit_profile: Edit profile
     export: Data export
+    import: Import
     preferences: Preferences
     settings: Settings
     two_factor_auth: Two-factor Authentication

config/locales/simple_form.en.yml

@@ -8,12 +8,15 @@ en:
         header: PNG, GIF or JPG. At most 2MB. Will be downscaled to 700x335px
         locked: Requires you to manually approve followers and defaults post privacy to followers-only
         note: At most 160 characters
+      imports:
+        data: CSV file exported from another Mastodon instance
     labels:
       defaults:
         avatar: Avatar
         confirm_new_password: Confirm new password
         confirm_password: Confirm password
         current_password: Current password
+        data: Data
         display_name: Display name
         email: E-mail address
         header: Header
@@ -24,6 +27,7 @@ en:
         otp_attempt: Two-factor code
         password: Password
         setting_default_privacy: Post privacy
+        type: Import type
         username: Username
       interactions:
         must_be_follower: Block notifications from non-followers

config/navigation.rb

@@ -9,6 +9,7 @@ SimpleNavigation::Configuration.run do |navigation|
       settings.item :preferences, safe_join([fa_icon('sliders fw'), t('settings.preferences')]), settings_preferences_url
       settings.item :password, safe_join([fa_icon('cog fw'), t('auth.change_password')]), edit_user_registration_url
       settings.item :two_factor_auth, safe_join([fa_icon('mobile fw'), t('settings.two_factor_auth')]), settings_two_factor_auth_url
+      settings.item :import, safe_join([fa_icon('cloud-upload fw'), t('settings.import')]), settings_import_url
       settings.item :export, safe_join([fa_icon('cloud-download fw'), t('settings.export')]), settings_export_url
       settings.item :authorized_apps, safe_join([fa_icon('list fw'), t('settings.authorized_apps')]), oauth_authorized_applications_url
     end

config/routes.rb

@@ -51,6 +51,7 @@ Rails.application.routes.draw do
   namespace :settings do
     resource :profile, only: [:show, :update]
     resource :preferences, only: [:show, :update]
+    resource :import, only: [:show, :create]
 
     resource :export, only: [:show] do
       collection do