Use labels for banner web_section_ids checkboxes so text its clickable

Now we can use the checkbox label text directly as locator at spec,
also default web_sections are created before every spec by loading
`db/seeds.rb` file so we were duplicating "Proposals" WebSection.

spec/system/admin/banners_spec.rb

@@ -73,7 +73,7 @@ describe "Admin banners magement" do
   end
 
   scenario "Publish a banner" do
-    section = create(:web_section, name: "proposals")
+    section = WebSection.find_by(name: "proposals")
 
     visit admin_root_path
 
@@ -92,7 +92,7 @@ describe "Admin banners magement" do
     fill_in "post_ended_at", with: next_week.strftime("%d/%m/%Y")
     fill_in "banner_background_color", with: "#850000"
     fill_in "banner_font_color", with: "#ffb2b2"
-    check "banner_web_section_ids_#{section.id}"
+    check section.name.titleize
 
     click_button "Save changes"