Added test for Redmine bug #2486.
Changes to trait validation: ensure mean is numerical, and don't try to check it's in range if it's blank.
Fix for Redmine bug #2486: ensure @new_covariates is non-empty if trait creation fails.
Added a test for Redmine bug #2486 for the case of editing a trait.
Fix for Redmine bug #2486 for the case where we are editing a trait.
Change to using dynamic title (c.f. Redmine issue #2599).