Add import of GGally

We need GGally for plotting compare.n plots
Add multi-chain analyses to analyse.rwty

Added and modified bits so that analyse.rwty will do compare.n analyses
and plots when called with more than one chain.
Added plots for compare.n

Added code to make GGally plots for compare.n analysis.
Updated testing code

Switched so that all code is using load.trees now, added sample code
for analyse.rwty.