[libcalamares] Move module-related things into subdirectory

- Currently just moves a single enum, but this is prep-work for
   moving the non-GUI parts of the module system into libcalamares,
   to better support GUI-less operation.

src/libcalamares/Typedefs.h

@@ -29,12 +29,6 @@ class Job;
 typedef QSharedPointer< Job > job_ptr;
 using JobList = QList< job_ptr >;
 
-enum ModuleAction : char
-{
-    Show,
-    Exec
-};
-
 class ViewStep;
 typedef QList< ViewStep* > ViewStepList;