Add more Layout Views

[Philipp-M]

There's still a lot of missing layout primitives.

This includes the more popular flex layout. I think source of inspiration could be taken from here: linebender/xilem#63 (relevant comment from Raph, which I at least with the current architecture, agree with).

A lot of inspiration can be taken from SwiftUI (which this architecture is mainly inspired of) and Jetpack Compose (this is probably more fitting as inspiration, since the layout model is adopted from that and Flutter).