Add WorldControlState msg type (#190)

* add serialized_state_v and world_control_state msg types

Signed-off-by: Ashton Larkin <ashton@openrobotics.org>

* add documentation

Signed-off-by: Ashton Larkin <ashton@openrobotics.org>

* use SerializedState instead of SerializedState_V in WorldControlState

Signed-off-by: Ashton Larkin <ashton@openrobotics.org>

* follow underscore naming convention

Signed-off-by: Ashton Larkin <ashton@openrobotics.org>

proto/ignition/msgs/world_control_state.proto

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2021 Open Source Robotics Foundation
+ *
+ * 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.
+ *
+*/
+
+syntax = "proto3";
+package ignition.msgs;
+option java_package = "com.ignition.msgs";
+option java_outer_classname = "WorldControlStateProtos";
+
+/// \ingroup ignition.msgs
+/// \interface WorldControlState
+/// \brief A message that allows for control of world functions, along with
+/// a serialized state that can represent the state of an
+/// entity-component-system (ECS)
+
+import "ignition/msgs/header.proto";
+import "ignition/msgs/serialized.proto";
+import "ignition/msgs/world_control.proto";
+
+message WorldControlState
+{
+  /// \brief Optional header data
+  Header header = 1;
+
+  /// \brief A WorldControl that allows for control of world functions
+  WorldControl world_control = 2;
+
+  /// \brief A SerializedState that can contain information about the
+  /// state of an entity-comonent-system (ECS)
+  SerializedState state = 3;
+};