Bring back the gazebo plugins (#1063)

The models and meshes are not included. We will need
to find an alternate way to reintegrate these and use them.

* Add simulation/gz_msgs back, and build with Gradle.

* Add back in the frc simulation plugins for gazebo.

* Add a new shared library, halsim_gazebo.

This library will become the interface between the
HAL sim layer and gazebo.

* Preserve the first channel number used in created Encoders in the Sim MockData.

This allows us to use the DIO channel number to connect with simulated encoders.

* Have the HAL Simulator set the reverse direction on creation.

This enables a simulator to be aware of the direction.

* Add a drive_motor plugin.

This is a bit of a 'magic' motor, which allows us to build robot
models that drive in a more realistic fashion.  It does this
by apply forces directly to the chassis, rather than relying on
the complex motion dynamics of a driven wheel.

This in turn allows the model to reduce wheel friction,
reducing scrub, and allowing for a more natural driving experience.

simulation/gz_msgs/src/include/simulation/gz_msgs/msgs.h

@@ -0,0 +1,47 @@
+/* This was originally auto generated by cmake.
+   However, it changes infrequently enough that it makes
+   sense to simply revise it by hand any time we change
+   the protobuf messages expressed in the .proto files */
+
+#ifndef _FRC_MSGS_H_
+#define _FRC_MSGS_H_
+
+#ifdef _WIN32
+  //include this before anything else includes windows.h
+  //putting this here saves putting it in more files
+  #include <Winsock2.h>
+#endif
+
+
+ #include "simulation/gz_msgs/bool.pb.h"
+ #include "simulation/gz_msgs/driver-station.pb.h"
+ #include "simulation/gz_msgs/float64.pb.h"
+ #include "simulation/gz_msgs/frc_joystick.pb.h"
+
+
+#include <gazebo/msgs/msgs.hh>
+#include <boost/shared_ptr.hpp>
+
+namespace gazebo {
+  namespace msgs {
+
+    typedef GzString String;
+
+    typedef boost::shared_ptr< gazebo::msgs::String > StringPtr;
+    typedef const boost::shared_ptr< const gazebo::msgs::String > ConstStringPtr;
+
+    typedef boost::shared_ptr< msgs::Float64 > Float64Ptr;
+    typedef const boost::shared_ptr< const msgs::Float64 > ConstFloat64Ptr;
+
+    typedef boost::shared_ptr< msgs::Bool > BoolPtr;
+    typedef const boost::shared_ptr< const msgs::Bool > ConstBoolPtr;
+
+    typedef boost::shared_ptr< msgs::FRCJoystick > FRCJoystickPtr;
+    typedef const boost::shared_ptr< const msgs::FRCJoystick > ConstFRCJoystickPtr;
+
+    typedef boost::shared_ptr< msgs::DriverStation > DriverStationPtr;
+    typedef const boost::shared_ptr< const msgs::DriverStation > ConstDriverStationPtr;
+  }
+}
+
+#endif /* _FRC_MSGS_H_ */

simulation/gz_msgs/src/main/proto/bool.proto

@@ -0,0 +1,15 @@
+package gazebo.msgs;
+
+/// \ingroup gazebo_msgs
+/// \interface Bool
+/// \brief A message for boolean data
+/// \verbatim
+
+option java_outer_classname = "GzBool";
+
+message Bool
+{
+  required bool data = 1;
+}
+
+/// \endverbatim

simulation/gz_msgs/src/main/proto/driver-station.proto

@@ -0,0 +1,21 @@
+package gazebo.msgs;
+
+/// \ingroup gazebo_msgs
+/// \interface DriverStation
+/// \brief A message for DriverStation data
+/// \verbatim
+
+option java_outer_classname = "GzDriverStation";
+
+message DriverStation
+{
+  required bool enabled = 1;
+  enum State {
+    AUTO = 0;
+    TELEOP = 1;
+    TEST = 2;
+  }
+  required State state = 2;
+}
+
+/// \endverbatim

simulation/gz_msgs/src/main/proto/float64.proto

@@ -0,0 +1,15 @@
+package gazebo.msgs;
+
+/// \ingroup gazebo_msgs
+/// \interface Float64
+/// \brief A message for floating point data
+/// \verbatim
+
+option java_outer_classname = "GzFloat64";
+
+message Float64
+{
+  required double data = 1;
+}
+
+/// \endverbatim

simulation/gz_msgs/src/main/proto/frc_joystick.proto

@@ -0,0 +1,16 @@
+package gazebo.msgs;
+
+/// \ingroup gazebo_msgs
+/// \interface Joystick
+/// \brief A message for joystick data
+/// \verbatim
+
+option java_outer_classname = "GzFRCJoystick";
+
+message FRCJoystick
+{
+  repeated double axes = 1;
+  repeated bool buttons = 2;
+}
+
+/// \endverbatim