This breaks the tests

We're switching to Jest anyways, and getting these things to run is basically impossible at the moment.

They rely on a working riot-web build, which this is not.

MatrixClientPeg in particular doesn't work very well with this.

With a switch to Only One Webpack™ we need a way to help developers generate the component index without a concurrent watch task. The best way to do this is to have developers import their components, but how do they do that when we support skins? The answer in this commit is to change skinning.

Skinning now expects to receive your list of overrides instead of the react-sdk+branded components. For Riot this means we send over *only* the Vector components and not Vector+react-sdk. 

Components can then be annotated with the `replaceComponent` decorator to have them be skinnable. The decorator must take a string with the dot path of the component because we can't reliably calculate it ourselves, sadly. 

The decorator does a call to `getComponent` which is where the important part of the branded components not including the react-sdk is important: if the branded app includes the react-sdk then the decorator gets executed before the skin has finished loading, leading to all kinds of fun errors. This is also why the skinner lazily loads the react-sdk components to avoid importing them too early, breaking the app.

The decorator will end up receiving null for a component because of the getComponent loop mentioned: the require() call is still in progress when the decorator is called, therefore we can't error out. All usages of getComponent() within the app are safe to not need such an error (the return won't be null, and developers shouldn't use getComponent() after this commit anyways).

The AuthPage, being a prominent component, has been converted to demonstrate this working. Changes to riot-web are required to have this work.

The reskindex script has also been altered to reflect these skinning changes - it no longer should set the react-sdk as a parent. The eventual end goal is to get rid of `getComponent()` entirely as it'll be easily replaced by imports.

We're making an assumption here that the decorator is actually all over the app when it's not.