Revert changes preventing old user code from compiling.

I'm not 100% sure whether we want these, but they are a quick
find and replace to do.

Basically, there are two primary things that we have done
this summer that break existing user code:
-Changing GetInstance() calls to return references instead
 of pointers. This forces users to change from doing something
 like LiveWindow::GetInstance()->AddSensor() to LiveWindow::GetInstance().AddSensor().
-Making PIDGet() and related calls const, forcing users to change
 the function signatures wherever they override them.

The GetInstance() calls don't really matter to me either way,
especially since there are no real ownership issues going on there,
unlike the rest of the smart pointer-related changes.

For the const stuff, it is certainly more correct to mandate that
user PIDGet() functions be const and the such, but at the same time,
I'm not sure that there is any strong need for it, and the errors
generated are not the most helpful. While this wouldn't necessarily
be an issue for more experienced teams or completely new teams (who
don't have any old code to be reusing), it may cause issues for more
average teams who aren't familiar with the intricacies of C++ anything.

Change-Id: I6e7007982069292ea70e6d0fc8ca40203340df1b

wpilibc/wpilibC++Devices/src/IterativeRobot.cpp

@@ -31,7 +31,7 @@ void IterativeRobot::StartCompetition() {
   HALReport(HALUsageReporting::kResourceType_Framework,
             HALUsageReporting::kFramework_Iterative);
 
-  LiveWindow &lw = LiveWindow::GetInstance();
+  LiveWindow *lw = LiveWindow::GetInstance();
   // first and one-time initialization
   SmartDashboard::init();
   NetworkTable::GetTable("LiveWindow")
@@ -46,14 +46,14 @@ void IterativeRobot::StartCompetition() {
   HALNetworkCommunicationObserveUserProgramStarting();
 
   // loop forever, calling the appropriate mode-dependent function
-  lw.SetEnabled(false);
+  lw->SetEnabled(false);
   while (true) {
     // Call the appropriate function depending upon the current robot mode
     if (IsDisabled()) {
       // call DisabledInit() if we are now just entering disabled mode from
       // either a different mode or from power-on
       if (!m_disabledInitialized) {
-        lw.SetEnabled(false);
+        lw->SetEnabled(false);
         DisabledInit();
         m_disabledInitialized = true;
         // reset the initialization flags for the other modes
@@ -67,7 +67,7 @@ void IterativeRobot::StartCompetition() {
       // call AutonomousInit() if we are now just entering autonomous mode from
       // either a different mode or from power-on
       if (!m_autonomousInitialized) {
-        lw.SetEnabled(false);
+        lw->SetEnabled(false);
         AutonomousInit();
         m_autonomousInitialized = true;
         // reset the initialization flags for the other modes
@@ -81,7 +81,7 @@ void IterativeRobot::StartCompetition() {
       // call TestInit() if we are now just entering test mode from
       // either a different mode or from power-on
       if (!m_testInitialized) {
-        lw.SetEnabled(true);
+        lw->SetEnabled(true);
         TestInit();
         m_testInitialized = true;
         // reset the initialization flags for the other modes
@@ -95,14 +95,14 @@ void IterativeRobot::StartCompetition() {
       // call TeleopInit() if we are now just entering teleop mode from
       // either a different mode or from power-on
       if (!m_teleopInitialized) {
-        lw.SetEnabled(false);
+        lw->SetEnabled(false);
         TeleopInit();
         m_teleopInitialized = true;
         // reset the initialization flags for the other modes
         m_disabledInitialized = false;
         m_autonomousInitialized = false;
         m_testInitialized = false;
-        Scheduler::GetInstance().SetEnabled(true);
+        Scheduler::GetInstance()->SetEnabled(true);
       }
       HALNetworkCommunicationObserveUserProgramTeleop();
       TeleopPeriodic();