[Bleeding] Added Conversations API. Addresses BUKKIT-864

By: rmichela <deltahat@gmail.com>

paper-api/src/main/java/org/bukkit/conversations/PlayerNamePrompt.java

@@ -0,0 +1,35 @@
+package org.bukkit.conversations;
+
+import org.bukkit.entity.Player;
+import org.bukkit.plugin.Plugin;
+
+/**
+ * PlayerNamePrompt is the base class for any prompt that requires the player to enter another player's name.
+ */
+public abstract class PlayerNamePrompt extends ValidatingPrompt{
+    private Plugin plugin;
+
+    public PlayerNamePrompt(Plugin plugin) {
+        super();
+        this.plugin = plugin;
+    }
+
+    @Override
+    protected boolean isInputValid(ConversationContext context, String input) {
+        return plugin.getServer().getPlayer(input) != null;
+        
+    }
+
+    @Override
+    protected Prompt acceptValidatedInput(ConversationContext context, String input) {
+        return acceptValidatedInput(context, plugin.getServer().getPlayer(input));
+    }
+
+    /**
+     * Override this method to perform some action with the user's player name response.
+     * @param context Context information about the conversation.
+     * @param input The user's player name response.
+     * @return The next {@link Prompt} in the prompt graph.
+     */
+    protected abstract Prompt acceptValidatedInput(ConversationContext context, Player input);
+}