NET-514 IMAP APPEND multiple issues in IMapClient.
Deprecated unusable append methods.
Added new append method, as well as example IMapImportMbox class to make use of it.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/net/trunk@1508693 13f79535-47bb-0310-9956-ffa450edef68