Book information: refactored and additional features

- Factored out duplicate code from filemanager.lua and filemanagerhistory.lua
to new filemanagerbookinfo.lua (and other common code to filemanagerutil.lua).
- Uses sidecar files' new doc_props and doc_pages settings, or fallback to
old 'stats' settings, or to opening document.
- Shows filename, filetype and directory.
- Shows description (Hold to see whole truncated text), keywords, and
cover image (tap to extract image from document and display it if available).
- Book information now available from reader menu, to display info about
the currently opened book.
- Convert possibly HTML description to plain text via added
util.htmlToPlainTextIfHtml() (for simple HTML conversion).

frontend/apps/reader/readerui.lua

@@ -10,6 +10,7 @@ local Device = require("device")
 local DocSettings = require("docsettings")
 local DocumentRegistry = require("document/documentregistry")
 local Event = require("ui/event")
+local FileManagerBookInfo = require("apps/filemanager/filemanagerbookinfo")
 local FileManagerHistory = require("apps/filemanager/filemanagerhistory")
 local Geom = require("ui/geometry")
 local InfoMessage = require("ui/widget/infomessage")
@@ -317,6 +318,12 @@ function ReaderUI:init()
         dialog = self.dialog,
         ui = self,
     })
+    -- book info
+    self:registerModule("bookinfo", FileManagerBookInfo:new{
+        dialog = self.dialog,
+        document = self.document,
+        ui = self,
+    })
     -- koreader plugins
     for _, plugin_module in ipairs(PluginLoader:loadPlugins()) do
         local ok, plugin_or_err = PluginLoader:createPluginInstance(