Unused bears show up in different categories (languages) on successive runs

On successive runs against `coala` repo, `print_relevant_bears` will display unused bears in different categories (languages) on each run. I think this is due to the fact that the filtering is done on a dictionary that is unordered (so on each run the values are eliminated in a different order, and for the values that belong to multiple categories/languages they might end up as flagged in different categories). This is blocked by https://github.com/coala/coala-quickstart/pull/227.

Start at the print_relevant_bears entry point and reproduce successive runs against the coala repository, comparing the categories assigned to unused bears. Review the filtering and its handling of dictionary iteration, then verify that repeated runs consistently display each bear in the expected category. This issue notes that work is blocked by coala-quickstart/pull/227.

Written by the indexing model from the issue text.