Just like we do every else (sometimes even on that very same file), we
use the method instead of the instance variable.
We're doing this change now because we're about to modify one of these
files (the poll question answers documents index component).
We were already using buttons to destroy pages from the pages index.
As mentioned in commits 5311daadf and bb958daf0, using links combined
with JavaScript to generate POST (or, in this case, DELETE) requests to
the server has a few issues.
This way we can simplify setting the title and styling the link in the
header. We're also fixing the unnecessary padding introduced by the
`column` classes, which caused the header not to be aligned with the
rest of the elements surrounding it. We're still keeping it the margin
used in the `row` classes so it's aligned with the rest of the form;
ideally, we would remove the `row` classes in the rest of the form and
in the whole admin section, but this isn't something we can tackle right
now.
Note that, in the CSS, the `margin-left: auto` property needs to be
included after `@include regular-button` because that mixin overwrites
the `margin-left` property. Since we're modifying this code, we're
making it compatible with RTL text, using `$global-left` instead of
`left`.
