Add popular-enabled option

This is similar to the removed `top-enabled` option but for the Popular feed.
The instance needs to be restarted if the feed was enabled.

Editing admin options on the preferences page is also fixed.

The handling of the feed pages now only happens in a single place.

Instead of redirecting:
  - The Top feed now displays a message that it was removed from Invidious.
  - The Popular feed now displays a message that it was disabled if it was.

src/invidious.cr

@@ -162,13 +162,16 @@ end
 Invidious::Jobs.register Invidious::Jobs::RefreshChannelsJob.new(PG_DB, logger, config)
 Invidious::Jobs.register Invidious::Jobs::RefreshFeedsJob.new(PG_DB, logger, config)
 Invidious::Jobs.register Invidious::Jobs::SubscribeToFeedsJob.new(PG_DB, logger, config, HMAC_KEY)
-Invidious::Jobs.register Invidious::Jobs::PullPopularVideosJob.new(PG_DB)
 Invidious::Jobs.register Invidious::Jobs::UpdateDecryptFunctionJob.new
 
 if config.statistics_enabled
   Invidious::Jobs.register Invidious::Jobs::StatisticsRefreshJob.new(PG_DB, config, SOFTWARE)
 end
 
+if config.popular_enabled
+  Invidious::Jobs.register Invidious::Jobs::PullPopularVideosJob.new(PG_DB)
+end
+
 if config.captcha_key
   Invidious::Jobs.register Invidious::Jobs::BypassCaptchaJob.new(logger, config)
 end
@@ -1140,13 +1143,20 @@ end
 
 get "/feed/top" do |env|
   locale = LOCALES[env.get("preferences").as(Preferences).locale]?
-  env.redirect "/"
+
+  message = translate(locale, "The Top feed has been removed from Invidious.")
+  templated "message"
 end
 
 get "/feed/popular" do |env|
   locale = LOCALES[env.get("preferences").as(Preferences).locale]?
 
-  templated "popular"
+  if config.popular_enabled
+    templated "popular"
+  else
+    message = translate(locale, "The Popular feed has been disabled by the administrator.")
+    templated "message"
+  end
 end
 
 get "/feed/trending" do |env|
@@ -2210,6 +2220,12 @@ get "/api/v1/popular" do |env|
 
   env.response.content_type = "application/json"
 
+  if !config.popular_enabled
+    error_message = {"error" => "Administrator has disabled this endpoint."}.to_json
+    env.response.status_code = 400
+    next error_message
+  end
+
   JSON.build do |json|
     json.array do
       popular_videos.each do |video|
@@ -2223,7 +2239,8 @@ get "/api/v1/top" do |env|
   locale = LOCALES[env.get("preferences").as(Preferences).locale]?
 
   env.response.content_type = "application/json"
-  "[]"
+  env.response.status_code = 400
+  {"error" => "The Top feed has been removed from Invidious."}.to_json
 end
 
 get "/api/v1/channels/:ucid" do |env|