Merge has_user_access?/4 args and pass entire object to has_user_access?/3

[rschef]

Closes #19

Current callback:

@callback has_user_access?(
    current_user,
    scope :: module(),
    {field :: any(), field_value :: any()},
    rule :: any()
  ) :: boolean()

• Merge scope module and {field, field_value} arguments into a struct, since scope module must define a struct
• Pass entire objects from field and query scope authorization to new has_user_access?/3
• Rename scope_by, scope_object_by and scope_field_by metas to scope?, scope_object? and scope_field?
• Set default scope? value to true