Event for theme

[BoiteBeet]

Add events in the theme switch so we can listen for them anywhere.
Nova.$emit('theme-changed', 'dark')

Right now I need to do an observer on the document.documentElement for the class 'dark' to be able to do it and it's really not the most performent.

It's particularily useful when developing components that needs some reloading for theme (i.e. some rich text fields like tinymce)

[gbrits]

Landed here because I needed the same thing.