New state classes

`montage--active` -> `is-active`. See issue: #1327
> Note: For the moment, the old classes are still kept for backwards compatibility

## Progress
- [x] Update [Naming Conventions](https://github.com/declarativ/docs.montagestudio.com/commit/693925374e56c966dee9d9f2f3c5f51969f4ba5c?short_path=e5a2f21#diff-e5a2f216e49b39c9d6cc143a83314399)
- [x] Update Abstract compents (this PR)

Once this PR is accepted, I'll update Digit + Matte