HTTP, MDN and general code optimization

1. Supports Java 7 and up. Java 6 (Java 1.6) is no longer supported.
2. Provide "log" command to dynamically alter logging levels in real time without restarting the application.
3. Rationalize MDN sending so that Synchronous and Asynchronous are processed by a single module. NB See upgrade notes for class name change.
4. Move HTTP header folding removal to HTTPUtils for centralised management
5. Make the HTTP "User-Agent" header configurable via a property.
6. Default "Message-Id" format complies with https://www.ietf.org/rfc/rfc2822.txt section 3.6.4.
7. Provide ability to configure emails for successfully received and sent files.
8. Upgrade libraries to the latest release.
9. Support using system environment variables in config.xml
10. Change attribute name for overriding Message-ID format at partnership level to match name at system level. NB See upgrade notes for attribute name change.
11. Allow modules to have scheduled tasks using the HasSchedule implementation.
12. Add scheduled task to detect failed sent messages where files are not cleaned up. (Fixes https://sourceforge.net/p/openas2/tickets/5/)
13. Allow attributes in partnership element to reference other partnership elements and resolve the references at load time.
14. Default sample in partnerships.xml for "as2_mdn_options" to use the "sign" attribute value for the micalg value.
15. Support AS2 ID with spaces in the value.