Created the mailbox class.

The mail box works liek a buffer with multiple queues
for each protocol. Similar to how JADE has multiple behaviours
that accept one kind of messages and ignores the others.
Reverted back to fields instead of subclasses

All the empty subclasses were removed and replaced my
a field in the ACLMessage class.
ACLmessage is not abstract now.

Also, i moved the constants to the ACL helper class.
Added mailbox support
Stuff and etc