Various fixes

[NicoPennec]

Problem

• When the search returns no results, the People Field widget may fail silently.
• Once authentication is successful, the login form briefly reappears before the home page loads.
• Some npm dependencies are outdated.

Solution

• Fix the silent PeopleField error when a search returns no results. vue-multiselect doesn't support a null value for items.
• Fix the brief flash of the login page after successful authentication.
• Bump npm dependencies.