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

plugins/messages/foodsoft_messages.gemspec

@@ -17,7 +17,9 @@ Gem::Specification.new do |s|
   s.test_files = Dir["test/**/*"]
 
   s.add_dependency "rails"
+  s.add_dependency "base32"
   s.add_dependency "deface", "~> 1.0.0"
+  s.add_dependency "mail"
 
   s.add_development_dependency "sqlite3"
 end