tagify: to support focusing with pseudo placeholders

Placeholder elements by use of absolutely positioned pseudo elements
need a special thing. Since absolutely positioned pseudos generate their
own box yet do not have a `focus` event, we need to force focus the
element on click. Pseudos fire `click` and it bubbles, fortunately.
Merge pull request #32 from behance/tagify-focus

tagify: to support focusing with pseudo placeholders