Widget sidebars not registering

For the main issue, see:
https://github.com/cuny-academic-commons/cbox-theme/issues/138

I've discovered that this is an Infinity issue.

The problem is:
https://github.com/cuny-academic-commons/cbox-theme/issues/138

`if ( current_theme_supports( 'infinity-sidebar-setup' ) )` was running too early and was returning `false` instead of `true`.

To remedy this, I've created a new function that is hooked to `'widgets_init'` and do our 'infinity-sidebar-setup' check and widget registration there.