Document preboot options for clarity

Minification is deprecated in version 6 of angular preboot. This leaves ssr-engine open to breaking changes in the future if it is not removed from all server examples. Not only this, but any change that angular introduce to preboot could introduce breaking changes. In a separate issue, I've recommend forking preboot and maintaining an aurelia version (https://github.com/aurelia/ssr-engine/issues/9). Also, either document or add an interface for the preboot options because it's a bit of a black box when the options are set in server.js in your project, then sent to the middleware, then sent to ssr-engine, then sent to the preboot transformer, then sent to preboot. Currently interfaces.ts in ssr-engine has no type information:

```
/**
* Options that are passed to preboot
*/
prebootOptions?: any;
```

Desired action: Remove breaking changes in the ssr skeletons, and add sufficient comments in the code as to how options are passed to preboot (which I should really be doing in my ssr fork). This should be in ssr-engine, middleware-koa and the ssr skeleton.

Start by reading interfaces.ts and the server.js examples to trace how prebootOptions move through ssr-engine, middleware-koa, the preboot transformer, and the SSR skeletons. Remove minification from the server examples and document the option flow and available type information; completion should cover ssr-engine, middleware-koa, and the SSR skeleton.

Written by the indexing model from the issue text.