Move logic out of CMakeLists.txt

This is an initial pass, simply moving the existing logic as-is. Future
PR's will attempt to refactor and improve the cmake stuff.

cMake/FreeCAD_Helpers/SetupMatplotlib.cmake

@@ -0,0 +1,13 @@
+macro(SetupMatplotlib)
+# ------------------------------ Matplotlib ------------------------------
+
+    find_package(Matplotlib)
+    if (MATPLOTLIB_FOUND)
+        message(STATUS "-- matplotlib-${MATPLOTLIB_VERSION} has been found.")
+    else(MATPLOTLIB_FOUND)
+        message("=====================================================\n"
+                "matplotlib not found, Plot module won't be available.\n"
+                "=====================================================\n")
+    endif(MATPLOTLIB_FOUND)
+
+endmacro(SetupMatplotlib)