Remove need for header clients to pluralize.
Update machine headers on add/remove.
Merge pull request #346 from kadams54/fix-mv-headers

### QA

1) With the `/:flags:/il/mv` active, switch to the machine view.
2) Deploy a bundle.
3) Ensure the machine column count is updated properly. Note that there's a known bug where the same machine will be rendered multiple times to the column, which has its own card. Nonetheless, the header should maintain the correct count.
4) Select a machine and make sure the container/unit header updates properly.

This branch fixes both the "Fix machine count…" and "Investigate using handlebars pluralize…" cards.