Add generic lead form widget.

This adds a new, generic lead form widget that will eventually replace the specific lead form widgets. I have tested this on the staging widget garden with Case's CMS. We need to merge this into master so that when Case launches and gets switched to the production widget garden, we won't lose this widget which is currently in use on their staging website.

This can safely exist on Madrona and other sites that use the older widgets because I have not yet removed them.