jekyll: move jekyll back to root, but simpler setup, exclude via _config.yml

app: bundle jekyll docs into app, add 'yarn run docs' to build
ui: add back/forward arrows for app only, adjust responsiveness for app, add IS_APP flag injected via preload
ui: add animated logo, friendly message on empty replay frame
app: improve serve logic:
- serve static files from static root
- serve replay from http localhost instead to avoid proxying https for remote requests
- serve local lookup from http prefix also
- catch any fallthrough from replay as 404
- add timestamp to response channels to ensure uniqness

docs/usage.md

@@ -0,0 +1,20 @@
+---
+layout: default
+title: Usage
+nav_order: 1
+description: 'Usage'
+has_children: true
+permalink: /docs/index.html
+---
+
+# ReplayWeb.Page
+## Serverless / Client-Side Web Archive Replay
+
+A browser-based system to replay archived web pages as accurately as possible, with all interactive elements preserved.
+{: .fs-6 .fw-300 }
+
+No server necessary. Archives can be loaded as static files from anywhere a browser can connect to.
+{: .fs-6 .fw-300 }
+
+
+