Renamed DelegatingPeerManager to CompositePeerManager, #21

This implementation doesn't act as a delegator, it's actually closer to
a composite.  It's not yet a true composite since it composes
PeerHandlers.
Refactored AbstractSwingPeerManager into a peer handler decorator, #21
Refactored AbstractSwtPeerManager into a peer handler decorator, #21
Centralised peer handler methods common across Swing/SWT, #21
Moved event loop from SwtWindowPeer to SwtPeerManager to resolve bug
introduced by decorating peer handlers, #21
Simplified symmetry-swing's MockPeerManager, #21
Renamed MockPeerManager to StubPeerManager since it returns canned
responses, #21
Moved symmetry-swing's StubPeerManager to symmetry-test-support, #21
Reused symmetry-test-support's StubPeerManager in symmetry-ui-swt, #21
Renamed PeerHandlerUtils to StateUtils and moved into subpackage, #21
Simplified StateUtils by using PropertyState, #21
Generalised StateUtils, #21
Fixed code style