Move Rails::Rack::Metal to Rails::Application::Metal and just add cascade if any metal was declared.

Refactor railties test, break huge  files in smaller chunks and move initializers to application folder.

PostgreSQLAdapter: set time_zone to UTC when Base.default_timezone == :utc so that Postgres doesn't incorrectly offset-adjust values inserted into TIMESTAMP WITH TIME ZONE columns [#3777 state:resolved]

Conflicts:
	railties/test/railties/plugin_test.rb

changed test to get TestMailer to use :file delivery method directly (as setup action was resetting delivery_method to :test on init

Added delivery_handler method to mail and implemented in ActionMailer to deliver inside of instrumentation

Add active_model/railtie back to generated boot.rb, add models back to paths, load active_support/railtie since we need it and ensure default logger is set before config.