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/Ports.elm

@@ -5,12 +5,14 @@ port module Ports exposing
     , onUiSettingsSaved
     , removeAccount
     , setAccount
+    , setUiTheme
     , storeUiSettings
     )
 
 import Api.Model.AuthResult exposing (AuthResult)
 import Data.Flags exposing (Flags)
 import Data.UiSettings exposing (StoredUiSettings, UiSettings)
+import Data.UiTheme exposing (UiTheme)
 
 
 {-| Save the result of authentication to local storage.
@@ -33,6 +35,14 @@ port requestUiSettings : ( AuthResult, StoredUiSettings ) -> Cmd msg
 port uiSettingsSaved : (() -> msg) -> Sub msg
 
 
+port internalSetUiTheme : String -> Cmd msg
+
+
+setUiTheme : UiTheme -> Cmd msg
+setUiTheme theme =
+    internalSetUiTheme (Data.UiTheme.toString theme)
+
+
 onUiSettingsSaved : msg -> Sub msg
 onUiSettingsSaved m =
     uiSettingsSaved (\_ -> m)