relax SVN archive

This follows from the thread at http://thread.gmane.org/gmane.science.nmr.relax.devel/7444.

The package will be used for assembling all of the data plotting capabilities of relax. It will
make support for different plotting software - Grace, OpenDX, matplotlib, gnuplot, etc - more
coherent. This will be used to create a software independent API for plotting in relax. I.e. the
plotting software is chosen by the user and then the data output by the user function passes into
the lib.plotting API which is then passed into the software dependent backend in lib.plotting.