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/widget/viewer/viewerdisplay.cpp

@@ -38,14 +38,14 @@
 #include <cstring>
 
 #include "audio/audiomanager.h"
-#include "common/define.h"
-#include "common/html.h"
+#include "oakutil/define.h"
+#include "common/htmlapp.h"
 #include "oakengine/gizmo.h"
 #include "oakengine/videoparams.h"
 #include "oakengine/display.h"
 #include "oakengine/undo.h"
 #include "widget/viewer/vieweroutpututils.h"
-#include "common/qtutils.h"
+#include "oakutil/qtutils.h"
 #include "common/configwrapper.h"
 #include "core.h"
 #include "node/block/subtitle/subtitle.h"

app/widget/viewer/viewerplaybacktimer.h

@@ -23,7 +23,7 @@
 
 #include <QtGlobal>
 
-#include "common/define.h"
+#include "oakutil/define.h"
 
 namespace olive
 {

app/widget/viewer/viewersafemargininfo.h

@@ -24,7 +24,7 @@
 
 #include <QtMath>
 
-#include "common/define.h"
+#include "oakutil/define.h"
 
 namespace olive
 {

app/widget/viewer/viewertexteditor.cpp

@@ -30,7 +30,7 @@
 #include <QTextBlock>
 #include <QtMath>
 
-#include "common/qtutils.h"
+#include "oakutil/qtutils.h"
 #include "ui/icons/icons.h"
 
 namespace olive