With this repo, you should be able to quickly get the designer tool at appmaker.mozillalabs.com/designer to load your custom component.
To use it:
# install node if you don't already have it
# install npm if the node installation didn't do it already
npm install -g grunt-init
git clone https://github.com/mozilla-appmaker/component-template.git
mkdir my-new-thing
cd my-new-thing
grunt-init ../component-template
npm install
#follow directions
grunt serve
# this will start a local server at http://localhost:9001
# go into appmaker, sign in, add a component giving the URL:
# http://localhost:9001/component.html