Add a shortcode for icons in html Editor field.

[hailwood]

It should convert [fa icon='star' classes='some extra classes'] into <i class="fa fa-star some extra classes"></i>)

Any attributes other than icon or classes should be passed along as is e.g. [fa icon="star" classes="another" title="A star"] would be <i class="fa fa-star another" title="A star"></i>

It should be optional (a register_shortcode option in the yml probably enabled by default)