bug-fixes: dealing with new status's

- disable audio and participant status dropdowns depending on
the selected option
- fix prev and next test button functionality
bug-fixes: more qa bug fixing

- completed status of test_entry wasnt being changed correctly
in test_enty db class
- first available test_entry to transcribe in a typist's
on-going assignment should not be deferred
- clean up prev/next getters in test_entry class