Update includes to to be relative to src directory

Don't use relative imports like `../foo.h` as those depend on the
relative position of both files. Rather than that use imports relative
to the `src` directory, which explicitly is part of the include
directories.

src/components/heartrate/Ppg.h

@@ -1,8 +1,8 @@
 #pragma once
 
 #include <array>
-#include "Biquad.h"
-#include "Ptagc.h"
+#include "components/heartrate/Biquad.h"
+#include "components/heartrate/Ptagc.h"
 
 namespace Pinetime {
   namespace Controllers {