Refactor all math into a new kimath library

* Split up the thirdparty code into the thirdparty folder (#3637)
* Create a new kimath static library containing all the math functions

This is part of cleaning the build system for #1906.

common/gr_basic.cpp

@@ -36,6 +36,7 @@
 #include <wx/graphics.h>
 #include <wx/tokenzr.h>
 #include <geometry/geometry_utils.h>
+#include <math/util.h>      // for KiROUND
 
 static const bool FILLED = true;
 static const bool NOT_FILLED = false;