Initial commit of plot wrapping updates.
Further wrapping updates to get Overlay plots defaulting to the correct coordinates, instead of -180 to 180.

Has an issue with countour and heatmap plots, due to rounding errors in the wrapped data.
Incorporated fix for plot wrapping when dealing with contours and heatmaps.  One issue was created due to rounding when using Iris wrap_lons function. Also required to use latlon as a plot arg to basemap only when using two dimensional data.
Fix for overlay plotting xmin and xmax defaults, with the new plot wrapping.
Documentation update for the overlay plotting with plot wrapping.