fix #1: incorrect path to vi
ui: fix unicode encoding error
fields: handle missing visibility_values, sortkey, name fields
bug: chase field name change platform -> rep_platform
fix #2: treat defaulted fields as mandatory

"Defaulted" fields are essentially mandatory if no default is
defined.  The Bugzilla API documentation states:

  Clients that want to be able to interact uniformly with multiple
  Bugzillas should always set both the params marked Required and
  those marked Defaulted, because some Bugzillas may not have
  defaults set for Defaulted parameters, and then this method will
  throw an error if you don't specify them.

Since there's currently no way to tell whether a field has a default
value, treat all defaulted fields as mandatory.  A possible
improvement would be to add a config allowing a user to tell us
which fields are defaulted.
bump version to v0.5.3