added image "spectrum" and created new image folder for "unit-testing"

Author: Josh4gitaboutit

public/docs/ts/latest/guide/unit-testing-01.jade

@@ -21,8 +21,10 @@ include ../../../../_includes/_util-fns
 
   There is considerable variety within functional testing, a spectrum from short, quick pure unit tests to long running end-to-end tests. We could classify them in broad groups
 
+figure.image-display
+  img(src='/resources/images/devguide/unit-testing/spectrum.png' alt="Functional Testing Spectrum")
 
-
+:markdown
   Pure unit test
   We test the part in isolation. Either the part  has no dependencies or we fake all of its dependencies during the test
   Close-in integration