Extract component to render a poll in the poll index

This is consistent with the way we've got partials to render debates,
proposals and legislation processes on their index pages.

Note that, while adding the tests for the status icon, we're keeping one
system test because it also tests the process of voting. We're adding a
new, similar component test, where the voter is created in the database,
so all possible statuses are tested in the component.

app/assets/stylesheets/polls/poll.scss

@@ -0,0 +1,86 @@
+.poll {
+  &.with-image {
+
+    @include breakpoint(medium) {
+      padding: 0 calc(#{$line-height} / 2) 0 0;
+    }
+
+    .image-container img {
+      height: 100%;
+      max-width: none;
+      position: absolute;
+    }
+  }
+
+  .icon-poll-answer {
+    border-top: 0;
+    border-bottom: 60px solid transparent;
+    height: 0;
+    position: absolute;
+    right: 0;
+    top: 0;
+    width: 0;
+
+    &.cant-answer::after,
+    &.not-logged-in::after,
+    &.already-answer::after,
+    &.unverified::after {
+      font-family: "icons" !important;
+      left: 34px;
+      position: absolute;
+      top: 5px;
+    }
+
+    &.cant-answer {
+      border-right: 60px solid $alert-bg;
+
+      &::after {
+        color: $color-alert;
+        content: "\74";
+      }
+    }
+
+    &.not-logged-in {
+      border-right: 60px solid $info-bg;
+
+      &::after {
+        color: $color-info;
+        content: "\6f";
+      }
+    }
+
+    &.unverified {
+      border-right: 60px solid $warning-bg;
+
+      &::after {
+        color: $color-warning;
+        content: "\6f";
+      }
+    }
+
+    &.already-answer {
+      border-right: 60px solid $success-bg;
+
+      &::after {
+        color: $color-success;
+        content: "\59";
+      }
+    }
+  }
+
+  .dates {
+    color: $text-medium;
+    font-size: $small-font-size;
+    margin-bottom: calc(#{$line-height} / 2);
+  }
+
+  h4 {
+    font-size: rem-calc(30);
+    line-height: $line-height * 1.5;
+
+    a {
+      color: inherit;
+      display: inline-block;
+    }
+  }
+}