Apply @RequiresCapability to REST API

Move the @RequiresCapability from SSHD to gerrit-extension-api. Modify
the RestApiServlet to check the current user has the required
capabilities. All RestApiServlets must now inject the currentUser
provider in their constructor and pass it to the super class.

Signed-off-by: Brad Larson <bklarson@gmail.com>
Change-Id: Iffc9bc99b8d2fafd07bf624008719b0ec647ce7d

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/annotations/RequiresCapability.java

@@ -0,0 +1,31 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.extensions.annotations;
+
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Annotation on {@link SshCommand} or {@link RestApiServlet} declaring a
+ * capability must be granted.
+ */
+@Target({ElementType.TYPE})
+@Retention(RUNTIME)
+public @interface RequiresCapability {
+  String value();
+}