Reuse ssr elements

[L3P3]

Allow lui to hydrate pre-rendered html and allow lui apps to be rendered into html code on the server, since some people NEED that.

[odincat]

This is indeed a very important and useful feature! I'm looking forward to a possible implementation. 😄

[L3P3]

Now, it is just replacing the ssr elements with newly created ones. Reusing the existing ones would be a feature but it is not that important for now.