Increased size of log files
Refactor of NXPlotView

In order to allow commands like ‘plotview.plot(…)’, instead of the
previously required ‘plotview.plot.plot(…)’, it was necessary to fold
the NXPlot class into NXPlotView. In fact, NXPlot added very little
extra functionality, so the refactoring made sense. This commit also
fixes a ‘new plot window’ bug.