Super fix

[xivh]

This pull request fixes the following bugs in casm super (#289):

1. casm super --scelnames scel1 --get-transf-mat crashes
2. casm super --scelnames scel1 --get-transf-mat --unitcell SCEL1_1_1_1_0_0_0 always returns the identity matrix
3. The --confignames and --scelnames options were only supposed to take one argument if --duper was not passed. This check was failing, so I fixed it, which also fixed some other --duper checks.

I also reformatted the --help output to match query.cc.

Two more comments:

1. By default, casm super --scelnames scel --transf-mat T or casm super --duper write to the supercell database, which I think should be optional. I can try to implement this if it sounds like a good idea.
2. The error handling is not consistent, e.g empty casm super --duper, casm super --get-transf-mat, and casm super --transf-mat all have different behavior. But, I think fixing this should be part of standardizing the app interfaces in general.