Added hooks in NodeEditorWindow for all mouse interactions with Nodes/Sockets.
Pedantic formatting.
Moved text showing current mouse position to the other side, as it was being obscured by the +/- buttons.
Bound the colour of socket labels to the colour of their corresponding socket.
Added isInput() and isOutput() convenience methods to NodeSocket.
Changed hover behaviour to make the colour lighter rather than darker.
Introduced Connection concept to manage relationship and representation of a connection between two Sockets.