minor cleanup on constants/

- removed/renamed one level of directories, not all constants are dimensioned
    global/dimensionedConstants -> global/constants/
    global/dimensionedConstants/constants/* -> global/constants/

- formatting and doxygen cleanup

- added degToRad() and radToDeg() inline functions (in mathematicalConstants)
  removed equivalent degToRad() from engineTime

src/engine/engineTime/engineTime.C

@@ -123,12 +123,6 @@ bool Foam::engineTime::read()
 }
 
 
-Foam::scalar Foam::engineTime::degToRad(const scalar deg) const
-{
-    return constant::mathematical::pi*deg/180.0;
-}
-
-
 Foam::scalar Foam::engineTime::degToTime(const scalar theta) const
 {
     // 6 * rpm => deg/s