Fix many errorprone warnings (#1247)

This fixes two real bugs:
- TimedRobot had a m_period that was hiding the IterativeRobotBase m_period
  and was not getting initialized.
- PDPSim was swapping two parameters to getCurrent()

wpilibj/src/main/java/edu/wpi/first/wpilibj/PIDBase.java

@@ -110,7 +110,7 @@ public class PIDBase extends SendableBase implements PIDInterface, PIDOutput {
   /**
    * Used internally for when Tolerance hasn't been set.
    */
-  public class NullTolerance implements Tolerance {
+  public static class NullTolerance implements Tolerance {
     @Override
     public boolean onTarget() {
       throw new IllegalStateException("No tolerance value set when calling onTarget().");