Allow to use the browser's pdf viewer

The viewerjs library has some limitations. Sometimes PDFs are quite
blurry and some content is displayed scrambled. Switching to the
browsers build-in PDF viewer (for chromium and firefox) fixes this. So
while on mobile the viewerjs is the only working viewer, for desktop
use it might be desireable to use the browsers builtin viewer instead.

modules/webapp/src/main/elm/Comp/ItemDetail.elm

@@ -35,7 +35,7 @@ import DatePicker exposing (DatePicker)
 import Dict exposing (Dict)
 import Html exposing (..)
 import Html.Attributes exposing (..)
-import Html.Events exposing (onClick, onInput)
+import Html.Events exposing (onCheck, onClick, onInput)
 import Http
 import Markdown
 import Page exposing (Page(..))
@@ -74,6 +74,7 @@ type alias Model =
     , sentMailsOpen : Bool
     , attachMeta : Dict String Comp.AttachmentMeta.Model
     , attachMetaOpen : Bool
+    , pdfNativeView : Bool
     }
 
 
@@ -160,6 +161,7 @@ emptyModel =
     , sentMailsOpen = False
     , attachMeta = Dict.empty
     , attachMetaOpen = False
+    , pdfNativeView = False
     }
 
 
@@ -212,6 +214,7 @@ type Msg
     | SentMailsResp (Result Http.Error SentMails)
     | AttachMetaClick String
     | AttachMetaMsg String Comp.AttachmentMeta.Msg
+    | TogglePdfNativeView
 
 
 
@@ -935,6 +938,11 @@ update key flags next msg model =
                 Nothing ->
                     ( model, Cmd.none )
 
+        TogglePdfNativeView ->
+            ( { model | pdfNativeView = not model.pdfNativeView }
+            , Cmd.none
+            )
+
 
 
 -- view
@@ -1206,6 +1214,17 @@ renderAttachmentView model pos attach =
                 , text (Util.Size.bytesReadable Util.Size.B (toFloat attach.size))
                 , text ")"
                 ]
+            , div [ class "item" ]
+                [ div [ class "ui slider checkbox" ]
+                    [ input
+                        [ type_ "checkbox"
+                        , onCheck (\_ -> TogglePdfNativeView)
+                        , checked model.pdfNativeView
+                        ]
+                        []
+                    , label [] [ text "Native view" ]
+                    ]
+                ]
             , div [ class "right menu" ]
                 [ a
                     [ classList
@@ -1234,7 +1253,7 @@ renderAttachmentView model pos attach =
                                     "Goto original file"
 
                          else
-                            "This is the original file"
+                            "The file was not converted."
                         )
                     , href (fileUrl ++ "/original")
                     , target "_new"
@@ -1269,7 +1288,11 @@ renderAttachmentView model pos attach =
                 ]
             ]
             [ iframe
-                [ src (fileUrl ++ "/view")
+                [ if model.pdfNativeView then
+                    src fileUrl
+
+                  else
+                    src (fileUrl ++ "/view")
                 ]
                 []
             ]