Generate context menu dynamically

Some dictionaries might be treated differently by assigning them some
value in the `contextCategory` property. This property can take two
values:

  - 'root', meaning that the dictionary will be added to the root of the
    context menu, with no extra categorization
  - A string identifying the category. This string will be used for
    localization, therefore it needs to be present in the `.properties`
    localization files. A sane value for this would be `context.Synonyms`
    for instance.