allowClear seems to be broken

Hello,

I am using both ember-power-select and ember-power-select-typehead.
In EPS `allowClear` works fine. The little cross is available and clicking it properly clear the selection.

However, in the typeahead version this parameter seems to have no effect. I've looked into the source
and the `allowClear` flag seems to be properly forwarded to EPS (see [this](https://github.com/cibernox/ember-power-select-typeahead/blob/master/addon/templates/components/power-select-typeahead.hbs#L52)).

Can you please advise? Thanks.

Start with the typeahead component template at addon/templates/components/power-select-typeahead.hbs, especially the allowClear forwarding referenced in the issue. Compare its behavior with ember-power-select, where clearing works, and reproduce the typeahead case to identify why the cross does not appear or clear the selection. Done means allowClear works in the typeahead component as it does in EPS.

Written by the indexing model from the issue text.