Fix for issue #1748: Student Interface: "0 missing required files" looks scary

**Issue**: #1748

**Problem**: "missing required files" appears in red when there are no missing files. It should not appear in red.

**Fix**: There is now a compound css class, `.info.red`, that styles the text to be red. The class `red` is only set if there are missing files.

**Testing**: Manual testing correctly shows that "missing required file(s)" is only red when count is > 0, for various locales.
```
bundle exec rake test
=> 982 tests, 2934 assertions, 2 failures, 25 errors, 0 skips
bundle exec rspec
=> 141 examples, 0 failures
```

*Note: I noticed that when changing locale to `/pt/`, english was still displayed. This was the case prior to my changes.*