Change Details

## Plan/AC ## * [] Add a feature manager class to the PHP codebase ** Provide a mechanism to register features, e.g. `$wgMFFeatures` config var * [] Add classes to the `head` or `body` element for the CSS codebase * [] Forward additional state to the client * [] Add a feature manager class to the JS codebase * [] Hydrate the state of the JS feature manager from the forwarded state

## Plan/AC ## * [] Add a feature manager class to the PHP codebase ** Provide a mechanism to register features, e.g. `$wgMFFeatures` config var * [] Add classes to the ~~`head`~~`html` or `body` element for the CSS code to target * [] Forward additional state to the client (via `mw.config` presumably) * [] Add a feature manager class to the JS codebase * [] Hydrate the state of the JS feature manager from the forwarded state (from `mw.config` presumably)

## Plan/AC ## * [] Add a feature manager class to the PHP codebase ** Provide a mechanism to register features, e.g. `$wgMFFeatures` config var * [] Add classes to the ~~`head``~~`html` or `body` element for the CSS codebase to target * [] Forward additional state to the client (via `mw.config` presumably) * [] Add a feature manager class to the JS codebase * [] Hydrate the state of the JS feature manager from the forwarded state (from `mw.config` presumably)