Subtree memorization / reactive templates (#488)

This commit adds subtree memoization to Dioxus.

Subtree memoization is basically a compile-time step that drastically 
reduces the amount of work the diffing engine needs to do at runtime by
extracting non-changing nodes out into a static "template." Templates 
are then understood by the various renderers in the ecosystem as a 
faster way of rendering the same items. 

For example, in the web, templates are simply a set of DOM Nodes created 
once and then cloned later. This is the same pattern frameworks like Lithtml
and SolidJS use to achieve near-perfect performance. 

Subtree memoization adds an additional level of complexity to Dioxus. The RSX
macro needs to be much smarter to identify changing/nonchanging nodes and
generate a mapping between the Template and its runtime counterparts.

This commit represents a working starter point for this work, adding support 
for templates for the web, desktop, liveview, ssr, and native-core renderers.
In the future we will try to shrink code generation, generally improve 
performance, and simplify our implementation.

packages/desktop/src/controller.rs

@@ -51,7 +51,7 @@ impl DesktopController {
                 dom.base_scope().provide_context(window_context);
 
                 // allow other proccesses to send the new rsx text to the @dioxusin ipc channel and recieve erros on the @dioxusout channel
-                #[cfg(feature = "hot-reload")]
+                #[cfg(any(feature = "hot-reload", debug_assertions))]
                 crate::hot_reload::init(&dom);
 
                 let edits = dom.rebuild();