fix(UserAccount): Fill `us_group` with the titles of `us_idgroup` (refs #4368)

When a user was added to a group, the user's `us_group` column was left
empty, and only `us_idgroup` was changed. With this correction, the
`us_group` column is filled with the titles of the groups from
`us_idgroup`.
Merge pull request #1049 from eguaj/3.2-A4368

fix(UserAccount): Fill `us_group` with the titles of `us_idgroup` (closes #4368)