Rename Poll::Question::Answer to Poll::Question::Option

Having a class named `Poll::Question::Answer` and another class named
`Poll::Answer` was so confusing that no developer working on the project
has ever been capable of remembering which is which for more than a few
seconds.

Furthermore, we're planning to add open answers to polls, and we might
add a reference from the `poll_answers` table to the
`poll_question_answers` table to property differentiate between open
answers and closed answers. Having yet another thing named answer would
be more than what our brains can handle (we know it because we did this
once in a prototype).

So we're renaming `Poll::Question::Answer` to `Poll::Question::Option`.
Hopefully that'll make it easier to remember. The name is also (more or
less) consistent with the `Legislation::QuestionOption` class, which is
similar.

We aren't changing the table or columns names for now in order to avoid
possible issues when upgrading (old code running with the new database
tables/columns after running the migrations but before deployment has
finished, for instance). We might do it in the future.

I've tried not to change the internationalization keys either so
existing translations would still be valid. However, since we have to
change the keys in `activerecord.yml` so methods like
`human_attribute_name` keep working, I'm also changing them in places
where similar keys were used (like `poll_question_answer` or
`poll/question/answer`).

Note that it isn't clear whether we should use `option` or
`question_option` in some cases. In order to keep things simple, we're
using `option` where we were using `answer` and `question_option` where
we were using `question_answer`.

Also note we're adding tests for the admin menu component, since at
first I forgot to change the `answers` reference there and all tests
passed.

spec/controllers/documents_controller_spec.rb

@@ -3,8 +3,8 @@ require "rails_helper"
 describe DocumentsController do
   describe "DELETE destroy" do
     context "Poll answers administration", :admin do
-      let(:current_answer) { create(:poll_question_answer, poll: create(:poll)) }
-      let(:future_answer) { create(:poll_question_answer, poll: create(:poll, :future)) }
+      let(:current_answer) { create(:poll_question_option, poll: create(:poll)) }
+      let(:future_answer) { create(:poll_question_option, poll: create(:poll, :future)) }
 
       it "is not possible for an already started poll" do
         document = create(:document, documentable: current_answer)
@@ -17,10 +17,10 @@ describe DocumentsController do
 
       it "is possible for a not started poll" do
         document = create(:document, documentable: future_answer)
-        request.env["HTTP_REFERER"] = admin_answer_documents_path(future_answer)
+        request.env["HTTP_REFERER"] = admin_option_documents_path(future_answer)
         delete :destroy, params: { id: document }
 
-        expect(response).to redirect_to admin_answer_documents_path(future_answer)
+        expect(response).to redirect_to admin_option_documents_path(future_answer)
         expect(flash[:notice]).to eq "Document was deleted successfully."
         expect(Document.count).to eq 0
       end