First version of new ui based on tailwind

This drops fomantic-ui as css toolkit and introduces tailwindcss. With
tailwind there are no predefined components, but it's very easy to
create those. So customizing the look&feel is much simpler, most of
the time no additional css is needed.

This requires a complete rewrite of the markup + styles. Luckily all
logic can be kept as is. The now old ui is not removed, it is still
available by using a request header `Docspell-Ui` with a value of `1`
for the old ui and `2` for the new ui.

Another addition is "dev mode", where docspell serves assets with a
no-cache header, to disable browser caching. This makes developing a
lot easier.

modules/webapp/src/main/webjar/docspell.js

@@ -25,6 +25,20 @@ var elmApp = Elm.Main.init({
     flags: elmFlags
 });
 
+elmApp.ports.internalSetUiTheme.subscribe(function(themeName) {
+    var body = document.getElementsByTagName("body");
+    if (body && body.length > 0) {
+        var bodyClasses = body[0].classList;
+        // seems that body attributes cannot be set from inside Elm.
+        if (themeName && themeName.toLowerCase() === 'dark') {
+            bodyClasses.add("bg-bluegray-800");
+            bodyClasses.add("dark");
+        } else {
+            bodyClasses.remove("bg-bluegray-800");
+            bodyClasses.remove("dark");
+        }
+    }
+});
 
 elmApp.ports.setAccount.subscribe(function(authResult) {
     console.log("Add account from local storage");