[poincare] Added framework to derivate unary functions, and implemented it for Sine

Added a method unaryFunctionDifferential to ExpressionNode and Expression, to be implemented by subclasses representing unary functions.
Added a function derivateUnaryFunction to Derivative, to factor (f°g)' -> g' * f'°g.

Change-Id: Id1780f1082ccd001f1282fe4ddfff2b7055d3a27

poincare/src/expression_node.cpp

@@ -131,6 +131,10 @@ bool ExpressionNode::didDerivate(ReductionContext reductionContext, Expression s
   return Expression(this).defaultDidDerivate();
 }
 
+Expression ExpressionNode::unaryFunctionDifferential() {
+  return Expression(this).defaultUnaryFunctionDifferential();
+}
+
 bool ExpressionNode::isOfType(Type * types, int length) const {
   for (int i = 0; i < length; i++) {
     if (type() == types[i]) {