Update to 2018_v4 image and new build system. (#598)

* Revert "Force OpenCV to 3.1.0 (#602)"

This reverts commit 50ed55e8e2.

* Removes Simulation

* Removes old build system

* Removes old gtest

* Adds new gmock and gtest

* Updates to new ni-libraries

* removes MyRobot (to be replaced)

* moves files to new location

* Adds new sim backend and new test executables

* updates .styleguide and .gitignore

* Changes cpp WPILibVersion to a function

MSVC throws an AV with the old version.

* Disables USBCamera on all systems except for linux

* 2018 NI Libraries

* New build system

wpilibc/src/main/native/include/PIDSource.h

@@ -0,0 +1,29 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2008-2017. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+namespace frc {
+
+enum class PIDSourceType { kDisplacement, kRate };
+
+/**
+ * PIDSource interface is a generic sensor source for the PID class.
+ * All sensors that can be used with the PID class will implement the PIDSource
+ * that returns a standard value that will be used in the PID code.
+ */
+class PIDSource {
+ public:
+  virtual void SetPIDSourceType(PIDSourceType pidSource);
+  PIDSourceType GetPIDSourceType() const;
+  virtual double PIDGet() = 0;
+
+ protected:
+  PIDSourceType m_pidSource = PIDSourceType::kDisplacement;
+};
+
+}  // namespace frc