sidebar support + pageview sidebar work!

- pages view now appears as sidebar in table/desktop sizes when clicking show pages button
- using <split-me> webcomponent to support adjustable splitter for sidebar
- pages view includes list filter if lists exist
- current page is highlighted when selected in sidebar
- date appears below url for each when in sidebar/mobile view mode

src/sorter.js

@@ -113,6 +113,7 @@ class Sorter extends LitElement
     return wrapCss(css`
       :host {
         min-width: 100px;
+        box-sizing: border-box !important;
       }
       button.button.is-small {
         border-radius: 4px;