Fix server-side validation

Closes #3122
-Fix validation so that all values are validated instead
 of just values that evaluate to true.
-Ensure validation methods consistently return promises
 and switch error handling from try/catch to promise.catch
 to get rid of unhandled rejection warnings.
-Add 0 and 1 to list of acceptable values in boolean validation.
Merge pull request #3124 from jaswilli/model-validation

Fix server-side validation