Initial Pcbnew s-expression file format commit.

* Add s-expression Format() function to all objects derived from
  BOARD_ITEM.
* Add s-expression Format() function to base objects as required.
* Add functions to convert coordinates from base internal units
  (nanometers) to millimeter string for writing to s-expression
  file.
* Add temporary dummy conversion functions to prevent link errors
  until schematic and board object and action code can be separated
  into DSO/DLL.
* Add CMake build option to build Pcbnew with nanometer internal
  units.

bitmap2component/bitmap2cmp_gui.cpp

@@ -426,3 +426,17 @@ bool EDA_APP::OnInit()
 void EDA_APP::MacOpenFile(const wxString &fileName)
 {
 }
+
+
+
+
+/**
+ * @copydoc
+ *
+ * This is a dummy since KiCad doesn't perform any interal unit formatting.
+ */
+/** @todo Remove FormatBIU() when the common DSO/DSL code is implemented. */
+std::string FormatBIU( int aValue )
+{
+    return "";
+}