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/common/xmlutilsapp.cpp

@@ -21,19 +21,19 @@
 // App-side implementation of xml_read_next_start_element
 // Provides a local definition so the app doesn't import this from liboakengine.
 
-#include "common/xmlutils.h"
+#include "oakutil/xmlutils.h"
 
 namespace olive
 {
 
 bool xml_read_next_start_element(QXmlStreamReader *reader,
-								CancelAtom *cancel_atom)
+								void *cancel_atom)
 {
 	QXmlStreamReader::TokenType token;
 
 	while ((token = reader->readNext()) != QXmlStreamReader::Invalid &&
 		   token != QXmlStreamReader::EndDocument &&
-		   (!cancel_atom || !cancel_atom->is_cancelled())) {
+		   (!cancel_atom)) {
 		if (reader->isEndElement()) {
 			return false;
 		} else if (reader->isStartElement()) {