add alternate model summary

This adds an alternate model summary that "more correctly" show the
model statuses at the cost of running significantly slower.  The old
summary is still available with the `--fast-model-summary` option.

Old:

Genome::Model::ReferenceAlignment
          Failed 1
         Running 37
     Unstartable 18
           Total 56

New:

Genome::Model::ReferenceAlignment
    Build Needed 30
         Running 26
           Total 56
Merge pull request #130 from nnutter/anp

add alternate model summary