removed redundant OBCocoa files / namespace; moved functions to UBPlatformUtils, which serves the same purpose

Application compiles and runs, with some caveats. Full list of changes:

- minor changes related to Qt4->Qt5 API differences

- Replaced calls to Carbon framework by Cocoa

- Removed registering of AE event handler. Seems to be done
automatically in Qt5.

- temporarily removed Podcast functionality, pending (presumably)
complete re-write due to Quicktime being obsolete in newer OS X
versions.

- Created OBCocoa namespace, and associated files src/core/OBCocoa.h/.mm, to
handle OS X - specific system calls. Currently used only by
UBApplication, but can in the future provide a useful interface between
the cocoa framework and OB, to avoid having too much OSX-specific code
in various files

update repository.

Long version:

UBGraphicsPolygonItem::shape() sometimes caused OpenBoard to crash due to
inifinite recursion. This is easily replicated by trying to use the
highlighting tool.

The reason is: shape() calls boundingRect(); this function's definition is:

     QRectF QGraphicsPolygonItem::boundingRect() const
     {
          Q_D(const QGraphicsPolygonItem);
          if (d->boundingRect.isNull()) {
              qreal pw = pen().style() == Qt::NoPen ? qreal(0) : pen().widthF();
              if (pw == 0.0)
                  d->boundingRect = d->polygon.boundingRect();
              else
                  d->boundingRect = shape().controlPointRect();
          }
          return d->boundingRect;
      }

In the case where pw != 0, the shape() function is called. However, it
is shape() from the derived class, not the base class, which is called.
In other words, UBGraphicsPolygonItem::shape() is called rather than
QGraphicsPolygonItem::shape().

This means that boundingRect() is called again from within shape(), and
so on, causing the program to crash.

The fix was simply to remove UBGraphicsPolygonItem::shape(), as it
appears to provide the same (or very similar) functionality to that of
the base class's shape() function.

In case this shape() function actually is needed, another workaround
should be implemented to prevent this infinite recursion.

Removed Linux-specific define (didn't work; the function wasn't defined when compiling on Linux, for some reason)

Q_WS_MACX -> Q_OS_OSX
Q_WS_MAC -> Q_OS_OSX
Q_WS_WIN -> Q_OS_WIN
Q_WS_X11 -> Q_OS_LINUX

Added loadAcquire() to get int value of QAtomicInt variables. (Was previously done automatically with the operatorint() of QAtomicInt)

added 'supportedDragActions' function to replace functionality provided by 'setSupportedDragActions' function (obsolete)