Throw OutOfMemory exception no memory for layers ImageSurface

Change for Bug #776346 comment 3: grey zombie canvas due to no memory for the layer's ImageSurface.  This change causes Pinta to check the status of the ImageSurface and throw an OutOfMemory exception if there is insufficient memory available for the ImageSurface.  I am handling this exception in all areas a document could be created and displaying an error message.  There are other areas in the code where layers are created and an OutOfMemory exception could be thrown and (currently) unhandled.