[Bleeding] Added Conversations API. Addresses BUKKIT-864

By: rmichela <deltahat@gmail.com>

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

@@ -0,0 +1,40 @@
+package org.bukkit.conversations;
+
+import org.apache.commons.lang.StringUtils;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * FixedSetPrompt is the base class for any prompt that requires a fixed set response from the user.
+ */
+public abstract class FixedSetPrompt extends ValidatingPrompt {
+    
+    protected List<String> fixedSet;
+
+    /**
+     * Creates a FixedSetPrompt from a set of strings.
+     * foo = new FixedSetPrompt("bar", "cheese", "panda");
+     * @param fixedSet A fixed set of strings, one of which the user must type.
+     */
+    public FixedSetPrompt(String... fixedSet) {
+        super();
+        this.fixedSet = Arrays.asList(fixedSet);
+    }
+
+    private FixedSetPrompt() {}
+
+    @Override
+    protected boolean isInputValid(ConversationContext context, String input) {
+        return fixedSet.contains(input);
+    }
+
+    /**
+     * Utility function to create a formatted string containing all the options declared in the constructor.
+     * The result is formatted like "[bar, cheese, panda]"
+     * @return
+     */
+    protected String formatFixedSet() {
+        return "[" + StringUtils.join(fixedSet, ", ") + "]";
+    }
+}