Rewrite of plot.qcc (from the qcc package) using ggplot and grid.

Provides a complete, seamless replacement for qcc's plot function. Nearly all of qcc's original plotting functionality has been implemented through ggplot2 and grid rather than base graphics.

Load library qcc, then source() the file qcc.plot.R. The qcc-native plotting function will be replaced in memory, and any future calls during the current session to plot() with a qcc object will utilize this function, including those calls from within qcc(). The resulting object can be re-used and modified within grid graphics.

plot.qcc() will require that the libraries ggplot2, grid and gtable be installed and available.

• Add back in the ability to control axis text orientation, using axes.las.
• Clean up the layout of the stats panel, especially when resizing to larger plot dimensions.