STYLE: changes to Time and TimeState

- update TimeState access methods

- use writeTime() instead of old method name outputTime()

- use deltaTValue() instead of deltaT().value()
  to avoids pointless construct of intermediate

src/functionObjects/doc/functionObjects.dox

@@ -68,7 +68,7 @@ functions
         timeEnd             10;
         evaluateControl     timeStep;
         evaluateInterval    1;
-        writeControl        outputTime;
+        writeControl        writeTime;
         writeInterval       1;
         ...
     }