[#53792115] Remove all traces of the `validating` status from the code.

- Fix the web responses UI so it works without `validating`
- Haven't touched mobile responses yet.
- This will probably break the build.
- (on web) incomplete response with errors > mark as complete > save as
  draft button is missing. This is because the `response` instance
variable has `status` set to `complete`, even though this isn't
persisted. Need to reload just this attribute.
[#53792115] Fix responses_spec
Remove this branch from travis
[#53792115] Make user_id and organization_id accessible (for a response).
[#53792115] Fix specs in answer_spec and response_serializer_spec.
[#53792115] Fix API::ResponsesController spec.
[#53792115] Add a spec to check that the mandatory validation is run for a web response.
[#53792115] Remove all occurrences of `validating` from the specs.
[#53792115] Set @disabled to false when the response edit page is rendered after an error.
[#53792115] Refactor the `update` methods in the response model.

- Add a method to update with conflict resolution
[#53792115] updating responses with conflicting resolution omits `status`
[#53792115] API::ResponsesController#update uses the new model method to update with conflict resolution.

- The model method was added in 5ce625f1994ec279fbab915af5a4dbd41d9b9a56
[#53792115] Refactor Response#create_valid_response_from_params.

- Instead of an explicit destroy, rely on the transaction
- When there's a validation error, the method returns false. This now happens by catching the `RecordInvalid` rethrown by the transaction.
- Rename it to create_response
[#53792115] Remove a redundant `if valid?` in the responses model.
[#53792115] Reload only the response's status when validation fails.

- In the regular ResponsesController#update.
[#53792115] Remove assignments of user_id and organization_id from the API::ResponsesController.