Add missing test data, fix add_rownames deprecation

[roryk]

Hi everyone,

The tests don't pass, but the same tests don't pass in master. This pull request does two things:

1. Includes the test data necessary for the tests to pass from https://github.com/cole-trapnell-lab/HSMMSingleCell
2. fixes the add_rownames deprecation warning by swapping the calls to be tibble::column_to_rownames instead.

[ctrapnell]

Thanks for this, @roryk. I realized I forgot to merge this before we passed the BioC 3.5 checkin deadline, and we're still fixing a few last minute things for the release. They ask that we not do anything other than fix docs and showstopper bugs in this release, but I will merge this as soon as the release is out. So it will be fixed in the next cycle. Sorry to be so slow, and thanks again for your help.