Based heavily on [s3-beam][1], but uses re-frame events/subs to get the job done. The /sign
handler is the [s3-beam][1] handler (near verbatim).
For background on (ui.core/component "...")
see https://opensourcery.co.za/2017/02/12/using-semantic-ui-react-with-re-frame/
ui.ajax
is just thin wrappers and/or aliases around plumbing from ajax.core
from cljs-http