disable the publish page button by default

[alhansrisuk]

Is your feature request related to a problem? Please describe.

If two articles have the same canonical URL Kiln allows both pages to be published before the Kiln JS Validator completes its checks. This results in two pages redirecting to the same canonical URL.

Describe the solution you'd like

Disable the publish button by default on load
https://github.com/clay/clay-kiln/blob/master/lib/drawers/publish-page.vue#L25