R8 phase 1: extract app/engine shared utilities into shared/include/oakutil

Move the pure-header utilities shared by app/ and engine/ out of
engine/common/ into a new shared/include/oakutil/ layer (define, lerp,
decibel, digit, range, crashpadutils, autoscroll, qtutils, filefunctions
declarations, and a trimmed xmlutils exposing a CancelAtom-free void*
overload). engine/common/ keeps forwarding headers so internal include
paths are unchanged; app/ now includes oakutil/* directly.

engine/node/project.h gains an explicit NodeGroup forward declaration
previously obtained transitively through the old xmlutils.h.

app/dialog/sequence/presetmanager.h

@@ -32,9 +32,9 @@
 #include <QXmlStreamReader>
 #include <QXmlStreamWriter>
 
-#include "common/define.h"
-#include "common/filefunctions.h"
-#include "common/xmlutils.h"
+#include "oakutil/define.h"
+#include "oakutil/filefunctions.h"
+#include "oakutil/xmlutils.h"
 
 namespace olive
 {

app/dialog/sequence/sequence.cpp

@@ -31,7 +31,7 @@
 #include <QVBoxLayout>
 
 #include "common/configwrapper.h"
-#include "common/qtutils.h"
+#include "oakutil/qtutils.h"
 #include "dialog/msgbox.h"
 #include "oakengine/node.h"
 #include "oakengine/timeline.h"

app/dialog/sequence/sequencepreset.h

@@ -25,7 +25,7 @@
 #include <olive/core/core.h>
 #include <QXmlStreamWriter>
 
-#include "common/xmlutils.h"
+#include "oakutil/xmlutils.h"
 #include "dialog/sequence/presetmanager.h"
 #include "render/videoparams.h"