Upgrade to Rails 6

- Added listen gem because rails app:update failed without it
- Removes nsa gem because it requires activesupport < 6
  Oddly, there's a newer version per GitHub that's not on RubyGems
  that raises the requirement to < 7. But, we need a new release
  before we can use that.
- Upgrade rails-i18n to v6, for Rails 6 compatibility
- Remove redis-rails since it requires Rails < 6, but we can just use
  the regular Rails :redis_cache_store that was introduced in 5.2.
- Run `rails app:update`
  - Had to weed through the `config/environments` changes to pick up
    newly added settings, while not losing settings that were
    intentionally configured
  - This generated config/initializers/new_framework_defaults_6_0.rb.
    The goal is to uncomment all of the settings in that file. Once
    they're all uncommented, delete the file and edit
    config/application.rb's load_defaults to be 6.0.
  - force_ssl controller method is deprecated in favor of a Rails
    config setting.
  - bin/setup was generated by Rails
  - Verbose query logging in development is really helpful. It shows
    you what line of code caused a query to execute.
  - Calling establish_connection after worker boot isn't necessary
    with ActiveRecord anymore. ActiveRecord handles it gracefully.
  - Rails generated a migration to add a foreign key for ActiveStorage.
    Gab currently doesn't use ActiveStorage, and instead uses Paperclip
    (since ActiveStorage didn't exist when Mastadon started). So, this
    change isn't relevant to Gab.
- Added ` || ''` in the profiles controller, because I was unable
  to save a change to a newly created profile. (This probably
  explains the 500 error I received on prod Gab recently.)

bin/setup

@@ -1,6 +1,5 @@
 #!/usr/bin/env ruby
 require 'fileutils'
-include FileUtils
 
 # path to your application root.
 APP_ROOT = File.expand_path('..', __dir__)
@@ -9,22 +8,25 @@ def system!(*args)
   system(*args) || abort("\n== Command #{args} failed ==")
 end
 
-chdir APP_ROOT do
-  # This script is a starting point to setup your application.
+FileUtils.chdir APP_ROOT do
+  # This script is a way to setup or update your development environment automatically.
+  # This script is idempotent, so that you can run it at anytime and get an expectable outcome.
   # Add necessary setup steps to this file.
 
   puts '== Installing dependencies =='
   system! 'gem install bundler --conservative'
   system('bundle check') || system!('bundle install')
-  system!('yarn install')
+
+  # Install JavaScript dependencies
+  # system('bin/yarn')
 
   # puts "\n== Copying sample files =="
   # unless File.exist?('config/database.yml')
-  #   cp 'config/database.yml.sample', 'config/database.yml'
+  #   FileUtils.cp 'config/database.yml.sample', 'config/database.yml'
   # end
 
   puts "\n== Preparing database =="
-  system! 'bin/rails db:setup'
+  system! 'bin/rails db:prepare'
 
   puts "\n== Removing old logs and tempfiles =="
   system! 'bin/rails log:clear tmp:clear'