R2S ALARA performance improvement

This PR adds a function (```record_to_geom```) to the ```alara``` module to create ALARA input files from ```dagmc.discretize_geom()``` record array output. This allows for smaller ALARA input files to be created in ```r2s.irradiation_setup()```. Basically, instead of every mesh volume element having its own ALARA mixture definition, mesh volume elements which contain similar mixtures share ALARA mixture definitions. This is perhaps easiest seen by looking at the changes to the expect output in ```tests/files_test_r2s/exp_alara_inp```.


The PR also takes care of some minor clean-up and a few additional options.