UPDATE: Adds web app (#79)

Things missing:

* Browse mode
* Front end tests
* Storybook

base/src/user_model/mod.rs

@@ -0,0 +1,12 @@
+#![deny(missing_docs)]
+
+mod common;
+mod history;
+mod ui;
+
+pub use common::UserModel;
+
+#[cfg(test)]
+pub use ui::SelectedView;
+
+pub use common::BorderArea;