Fix an undefined variable notice

Fixes the notice ‘PHP Notice:  Undefined variable: help_class in
/WordPress-Admin-Help/class-screen-admin.php on line 664’
Merge pull request #42 from JDGrimes/undefined-var-notice

Fix an undefined variable notice, thanks @jdgrimes!
Make the default for the overviews consistently off

Fixes #43
Merge pull request #44 from JDGrimes/issue-43

Make the default for the overviews consistently off -- thanks @jdgrimes!
version bump and changelog
added @jdgrimes as a contributor