Move require.js's data-main configuration script inline

require.js loads data-main asynchronously, so our inline javascript to
instantiate widgy sometimes runs before require is configured. This
results in require not being able to find libraries, and widgy fails to
start. This fixes the intermittent 'blank widgy editor' bug.

Also fixes a hardcoding of `/static/` paths when `{% static %}` should
be used instead.