Add handling for message reply via email

If the reply_email_domain configuration is set the messages plugin will
use unique Reply-To addresses for every email. They contain enough
information to reconstruct the message context and a hash to avoid
user forgery and spam.
A mail transfer agent must be configured to call the new rake task
foodsoft:parse_reply_email for incoming mails. The rake task requires
the receipt of the mail in the RECIPIENT variable and the raw message
via standard input. An example invocation would look like:
rake foodsoft:parse_reply_email RECIPIENT=f.1.1.HASH < test.eml

lib/foodsoft_config.rb

@@ -80,6 +80,10 @@ class FoodsoftConfig
       setup_database
     end
 
+    def select_multifoodcoop(foodcoop)
+      select_foodcoop foodcoop if config[:multi_coop_install]
+    end
+
     # Return configuration value for the currently selected foodcoop.
     #
     # First tries to read configuration from the database (cached),
@@ -134,15 +138,20 @@ class FoodsoftConfig
       keys.map(&:to_s).uniq
     end
 
+    # @return [Array<String>] Valid names of foodcoops.
+    def foodcoops
+      if config[:multi_coop_install]
+        APP_CONFIG.keys.reject { |coop| coop =~ /^(default|development|test|production)$/ }
+      else
+        config[:default_scope]
+      end
+    end
+
     # Loop through each foodcoop and executes the given block after setup config and database
     def each_coop
-      if config[:multi_coop_install]
-        APP_CONFIG.keys.reject { |coop| coop =~ /^(default|development|test|production)$/ }.each do |coop|
-          select_foodcoop coop
-          yield coop
-        end
-      else
-        yield config[:default_scope]
+      foodcoops.each do |coop|
+        select_multifoodcoop coop
+        yield coop
       end
     end