Adds basic plugin dependencies, courtesy of Raphfrk

By: Dinnerbone <dinnerbone@dinnerbone.com>

paper-api/src/main/java/org/bukkit/plugin/UnknownDependencyException.java

@@ -0,0 +1,63 @@
+
+package org.bukkit.plugin;
+
+/**
+ * Thrown when attempting to load an invalid Plugin file
+ */
+public class UnknownDependencyException extends Exception {
+
+    private static final long serialVersionUID = 5721389371901775894L;
+    private final Throwable cause;
+    private final String message;
+
+    /**
+     * Constructs a new UnknownDependencyException based on the given Exception
+     *
+     * @param throwable Exception that triggered this Exception
+     */
+    public UnknownDependencyException(Throwable throwable) {
+        this(throwable, "Unknown dependency");
+    }
+
+    /**
+     * Constructs a new UnknownDependencyException with the given message
+     *
+     * @param message Brief message explaining the cause of the exception
+     */
+    public UnknownDependencyException(final String message) {
+        this(null, message);
+    }
+
+    /**
+     * Constructs a new UnknownDependencyException based on the given Exception
+     *
+     * @param message Brief message explaining the cause of the exception
+     * @param throwable Exception that triggered this Exception
+     */
+    public UnknownDependencyException(final Throwable throwable, final String message) {
+        this.cause = null;
+        this.message = message;
+    }
+
+    /**
+     * Constructs a new UnknownDependencyException
+     */
+    public UnknownDependencyException() {
+        this(null, "Unknown dependency");
+    }
+
+    /**
+     * If applicable, returns the Exception that triggered this Exception
+     *
+     * @return Inner exception, or null if one does not exist
+     */
+    @Override
+    public Throwable getCause() {
+        return cause;
+    }
+
+    @Override
+    public String getMessage() {
+        return message;
+    }
+}