login: missing parameters are 400s

Dependencies

• [2] WDKFN4B2 Make sign in a modal dialog box rather than a separate page
• [3] LZVO64YG Merge in the first bits of the API work
• [4] XJRJ4J7M Add user registration

Change contents

• replacement in src/lib/Hydra/Controller/User.pm at line 30
  [3.24002]→[2.117:250](∅→∅)
  − error($c, "You must specify a user name.") if $username eq "";

  − error($c, "You must specify a password.") if $password eq "";
  [3.24002]

  [3.877]
  + badRequest($c, "You must specify a user name.") if $username eq "";

  + badRequest($c, "You must specify a password.") if $password eq "";