DisplayManager refactor for version 1.1

[gwaldron]

Friends, we've pushed an update with a refactoring of the DisplayManager subsystem. The goal here is to make typical "window with one or more inset views" easier to manage and navigate, since doing so in "pure VSG" can get tricky if you are not a Vulkan expert.

Hopefully it's all self-explanatory but check out the demos and feel free to ask questions :) -g

[Vic-Min]

Compile error after DisplayManager refactor #217

[GaussGun3000]

not sure if #220 belongs here but it might be related to the topic