Add templates for bootstrap's horizontal forms

Bootstrap's form-horizontal requires a little different HTML
structure than the default horiozn's field template uses. This
patch adds a _horizontal_fields.html template, that behaves like
the _form_fields.html template, only is suitable for use inside
a <form class="form-horizontal"> tag.

It also splits out the _form_errors.html, _form_field.html and
_horizontal_field.html templates, so that it is easier to build custom
forms with fieldsets by including those for every field, instead of all
the fields at once.

Change-Id: I51c8f47ba230c6a78919979cc0ef4e2383d100ba
Implements: blueprint horizontal-form
Merge "Add templates for bootstrap's horizontal forms"