ENH: support frequency or period for Sine/Square Function1 (#1917)

- For slow oscillations it can be more intuitive to specify the
  period.

ENH: separate mark/space for Square

- makes it easier to tailor the desired intervals.

BUG: incorrect square wave fraction with negative phase shifts

ENH: additional cosine Function1

STYLE: avoid code duplication by inheriting Cosine/Square from Sine.

tutorials/compressible/rhoPimpleFoam/laminar/sineWaveDamping/0/p

@@ -23,11 +23,10 @@ boundaryField
 {
     inlet
     {
-        type            uniformFixedValue; // oscillatingFixedValue;
+        type            uniformFixedValue;
         uniformValue    sine;
         uniformValueCoeffs
         {
-            amplitude       constant 1;
             frequency       constant 3000;
             scale           constant 50;
             level           constant 101325;