[ReviewEntries] Cannot save entries without gloss even with definition

[imnasnainaec]

In review entries, we intentionally don't allow entries to be saved without a gloss. (There's an exception is for protected entries, since they cannot be deleted.) However, if entries were imported with definitions instead of glosses (e.g., from WeSay) but aren't protected, then users cannot edit and save them.

Action items:

• Allow saving entries if gloss OR definition is nonempty
• Add corresponding string to "reviewEntries.error.gloss" ("Glosses cannot be left blank") for projects with definitions (e.g., "Glosses and definitions cannot both be left blank")