Add a display property for linking to users.

Issue #424

api/src/main/java/com/dmdirc/events/DisplayProperty.java

 
 package com.dmdirc.events;
 
+import com.dmdirc.interfaces.User;
 import com.dmdirc.util.colours.Colour;
 
 /**
- * Describes a property that may be set on a {@link DisplayableEvent} to affect its display.
+ * Describes a property that may be set on a {@link com.dmdirc.interfaces.Displayable} to affect its display.
  */
 @SuppressWarnings("UnusedDeclaration") // Generic type used for compile-time validation only
 public interface DisplayProperty<T> {
     DisplayProperty<Boolean> DO_NOT_DISPLAY = new DisplayPropertyImpl<>();
     /** Whether to suppress timestamps for the event. */
     DisplayProperty<Boolean> NO_TIMESTAMPS = new DisplayPropertyImpl<>();
+    /** A user that the displayable is linked to. */
+    DisplayProperty<User> LINK_USER = new DisplayPropertyImpl<>();
 
     final class DisplayPropertyImpl<T> implements DisplayProperty<T> {}
 

src/main/java/com/dmdirc/ChannelClient.java

         this.groupChat = groupChat;
         this.clientInfo = clientInfo;
         properties = new DisplayPropertyMap();
+        properties.put(DisplayProperty.LINK_USER, user);
     }
 
     @Override