fdo#81237: 2D OpenGL charts have wrong size

So far the size unit was 100th mm \ OPENGL_SCALE_VALUE
which is an absolute value, independent from the actual
size of the OpenGL window.
To solve that I added the SetSizePixel() method with
which we can specify the size in pixels and which
method resize the whole scene accordingly.

Change-Id: Ibd19a1bd9484c7bc8f8ce0d8113f60b95619db39
fdo#81237: OpenGL window is not resized by view change

Reproduce:
- Create a 2D OpenGL chart
- Step out from edit mode
- Zoom in / zoom out

Behavior
- Chart window is not resized, it has a constant size.

When we step out from chart edit mode the chart becomes
an inplace active object (instead of UI active) which means
the m_xDockingAreaAcceptor is removed. On the other hand
it seems we don't actually use this m_xDockingAreaAcceptor here,
so don't need to check whether it exists.

Change-Id: I056109b6e5cac28cdd2aeb8fabd9190413a16ed5
OPENGL_SCALE_VALUE is not needed any more

It seems to me that this value was a workaround to
make chart fit to the OpenGL window (working in calc, in default view).
Now it's uselss since projection matrix do this job better.

Change-Id: I968d6d96cb45c2444b8ebed59830b87f0cb87b61