make auto crop default be page content

Based on:

```
function ReaderCropping:setCropZoomMode(confirmed)
    if confirmed then
        -- if original zoom mode is "page???", set zoom mode to "content???"
        local zoom_mode_type = self.orig_zoom_mode:match("page(.*)")
        self:setZoomMode(zoom_mode_type
                    and "content"..zoom_mode_type
                    or self.orig_zoom_mode)
        self.ui:handleEvent(Event:new("InitScrollPageStates"))
    else
        self:setZoomMode(self.orig_zoom_mode)
    end
end
```

frontend/apps/reader/modules/readercropping.lua

@@ -21,8 +21,6 @@ function ReaderCropping:onPageCrop(mode)
     -- backup original zoom mode as cropping use "page" zoom mode
     self.orig_zoom_mode = self.view.zoom_mode
     if mode == "auto" then
-        --- @fixme: This is weird. "auto" crop happens to be the default, yet the default zoom mode/genus is "page", not "content".
-        ---         This effectively yields different results whether auto is enabled by default, or toggled at runtime...
         if self.document.configurable.text_wrap ~= 1 then
             self:setCropZoomMode(true)
         end

frontend/apps/reader/modules/readerzooming.lua

@@ -240,6 +240,12 @@ function ReaderZooming:onReadSettings(config)
         zoom_mode = self.zoom_mode_label[zoom_mode] and zoom_mode or self.DEFAULT_ZOOM_MODE
     end
 
+    -- auto crop needs to be page content
+    local trim_page = config:readSetting("kopt_trim_page")
+                             or G_reader_settings:readSetting("kopt_trim_page") or G_defaults:readSetting("DKOPTREADER_CONFIG_TRIM_PAGE")
+    local temp_zoom_mode = zoom_mode:match("page(.*)")
+    zoom_mode = trim_page == 1 and temp_zoom_mode and "content"..temp_zoom_mode or zoom_mode
+
     -- Import legacy zoom_factor settings
     if config:has("zoom_factor") and config:hasNot("kopt_zoom_factor") then
         config:saveSetting("kopt_zoom_factor", config:readSetting("zoom_factor"))