Add the Function and trig functions classes and layout.

We create an abstraction for functions with the function class.

Change-Id: Ia52f38da2ab3fb6781ad77c1b909676c53a4f424

poincare/src/function.cpp

@@ -0,0 +1,10 @@
+#include <poincare/function.h>
+#include "layout/function_layout.h"
+
+Function::~Function() {
+  delete m_arg;
+}
+
+ExpressionLayout * Function::createLayout(ExpressionLayout * parent) {
+  return new FunctionLayout(parent, m_function_name, m_arg);
+}