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/elm/Comp/Progress.elm

@@ -1,5 +1,6 @@
 module Comp.Progress exposing
-    ( smallIndicating
+    ( progress2
+    , smallIndicating
     , topAttachedIndicating
     )
 
@@ -7,6 +8,21 @@ import Html exposing (Html, div, text)
 import Html.Attributes exposing (attribute, class, style)
 
 
+progress2 : Int -> Html msg
+progress2 percent =
+    div [ class "shadow w-full h-full bg-gray-200 dark:bg-bluegray-600 rounded relative" ]
+        [ div
+            [ class "transition-duration-300 h-full bg-blue-500 dark:bg-light-blue-500 block text-xs text-center"
+            , style "width" (String.fromInt percent ++ "%")
+            ]
+            []
+        , div [ class "absolute left-1/2 -top-1 font-semibold" ]
+            [ text (String.fromInt percent)
+            , text "%"
+            ]
+        ]
+
+
 smallIndicating : Int -> Html msg
 smallIndicating percent =
     progress "small indicating active" percent Nothing Nothing