Convert Twig-based "slug" field into Vue component.

[bobdenotter]

Currently, the "slug" field is generated in HTML. Code for the field is here: https://github.com/bobdenotter/symfony-skeleton/blob/master/templates/editcontent/fields/slug.twig

Ideally, this field should be converted to a nice, self-contained Vue component, that's easier to maintain.

Current JS code entry point is here: https://github.com/bobdenotter/symfony-skeleton/blob/master/assets/js/bolt.js

Build instructions are in README.md. After setting up, you should be able to log on to the Admin Panel, at /bolt, and from the Dashboard click on "Edit" on any of the dummy records to go to the Edit page.

Note: the current code is very prototype-y. Feel free to re-arrange stuff, if it makes more sense. :-)

[jackiboy]

@bobdenotter you can close this badboy

[bobdenotter]

Fixed in #26