update __getattr__ for FrozenPotWrapper
freeze one of the spins in xy_model_system

this eliminates the global rotational invariance
supress long strings when printing system properties

plus a few samll updates
TSGraph now won't modify the database

functions addMinimum and addTransitionState and mergeMinima will now
only change what is in the graph.  The database must be updated manually
image_density and iter_density are now floats

instead of integers
speed up the creation of the transition state graph
mylbfgs will use default H0 if the passed H0 is negative

it was calling STOP and killing the program before
ensure number of NEB images is at least 3
minor changes
the disconnectivity graph gui now uses a color selector

it uses a QColorDialog rather than a drop down list of colors.
start to add a tool for coloring disconnectivity graphs
reorganize the coloring algorithm
dgraph.color_by_group is basically finished
add dgraph tests to run_test
add DisconnectivityGraph.color_by_value

which colors the graph by values associated with minima, e.g. order
parameter
add function DisconnectivityGraph.label_minima()

this function adds an xtick at the bottom of the graph with a specified
label
change dgraph colormap
add labeling minia on right click to dgraph gui
can now change line width and title in dgraph gui
clean up tests for rates.

also add some comments and do some sanity checking at the start.

I'm starting to add support for product and reactant groups larger than
1