Merge remote-tracking branch 'origin/receiverComponent'

This branch refactors the previously contributed "server" and
"remote" components such that they now extend a common "receiver"
component.  A receiver is a component that receives logging
events from a remote appender.  A connection between and an
appender and a receiver may be initiated in either direction;
i.e. a receiver may initiate the connection to an appender or
vice-versa.  The receiver component is configured in Joran using
a <receiver> element.  The class specified in this element
determines whether the receiver will passively await connections
from remote appenders (i.e. as in the legacy SimpleSocketServer)
or whether it will initiate a connection to a remote appender
(a ServerSocketAppender).