[libcalamares] Simplify includes

- CalamaresVersion used by the job, not the API presented to Python.
 - Untangle Qt includes from there.

src/libcalamares/PythonJob.cpp

@@ -19,6 +19,7 @@
 
 #include "PythonJob.h"
 
+#include "CalamaresVersion.h"
 #include "GlobalStorage.h"
 #include "JobQueue.h"
 #include "PythonHelper.h"

src/libcalamares/PythonJobApi.h

@@ -20,9 +20,7 @@
 #ifndef PYTHONJOBAPI_H
 #define PYTHONJOBAPI_H
 
-#include "CalamaresVersion.h"
-
-#include "PythonJob.h"
+#include "qglobal.h"  // For qreal
 
 #undef slots
 #include "utils/boost-warnings.h"
@@ -32,6 +30,11 @@
 #pragma clang diagnostic pop
 #endif
 
+namespace Calamares
+{
+class PythonJob;
+}
+
 namespace CalamaresPython
 {