[bug 917779] Give Firefox OS some space

* change "FirefoxOS" to "Firefox OS" across the project
* data migration to convert "FirefoxOS" to "Firefox OS" in platform
  field
* fix browser detection to not add .0 to end of Firefox OS versions
* add tests for all Firefox OS user agents plus one non-sensical one
* data migration to convert non-sensical Firefox OS versions to ''

To test:

1. run the tests with `FORCE_DB=1`
2. run the migrations
3. reindex
4. click through the dashboard and make sure the facet values and data look ok

r?