[UX] Gesture manager: add action - show book information (#4777)

As requested by @ersi.

Cf. https://github.com/koreader/koreader/issues/4727#issuecomment-471766024

frontend/apps/filemanager/filemanagerbookinfo.lua

@@ -28,16 +28,7 @@ function BookInfo:addToMainMenu(menu_items)
     menu_items.book_info = {
         text = self.bookinfo_menu_title,
         callback = function()
-            -- Get them directly from ReaderUI's doc_settings
-            local doc_props = self.ui.doc_settings:readSetting("doc_props")
-            -- Make a copy, so we don't add "pages" to the original doc_props
-            -- that will be saved at some point by ReaderUI.
-            local book_props = {}
-            for k, v in pairs(doc_props) do
-                book_props[k] = v
-            end
-            book_props.pages = self.ui.doc_settings:readSetting("doc_pages")
-            self:show(self.document.file, book_props)
+            self:onShowBookInfo()
         end,
     }
 end
@@ -203,4 +194,17 @@ function BookInfo:show(file, book_props)
     UIManager:show(widget)
 end
 
+function BookInfo:onShowBookInfo()
+    -- Get them directly from ReaderUI's doc_settings
+    local doc_props = self.ui.doc_settings:readSetting("doc_props")
+    -- Make a copy, so we don't add "pages" to the original doc_props
+    -- that will be saved at some point by ReaderUI.
+    local book_props = {}
+    for k, v in pairs(doc_props) do
+        book_props[k] = v
+    end
+    book_props.pages = self.ui.doc_settings:readSetting("doc_pages")
+    self:show(self.document.file, book_props)
+end
+
 return BookInfo

frontend/apps/reader/modules/readergesture.lua

@@ -36,6 +36,7 @@ local action_strings = {
     toc = _("Table of contents"),
     bookmarks = _("Bookmarks"),
     reading_progress = _("Reading progress"),
+    book_info = _("Book information"),
     book_status = _("Book status"),
 
     history = _("History"),
@@ -320,6 +321,7 @@ function ReaderGesture:buildMenu(ges, default)
         { "toc", not self.is_docless},
         {"bookmarks", not self.is_docless},
         {"reading_progress", ReaderGesture.getReaderProgress ~= nil},
+        {"book_info", not self.is_docless},
         {"book_status", not self.is_docless, true},
 
         {"history", true},
@@ -623,6 +625,8 @@ function ReaderGesture:gestureAction(action, ges)
         self.ui:handleEvent(Event:new("ShowBookmark"))
     elseif action == "history" then
         self.ui:handleEvent(Event:new("ShowHist"))
+    elseif action == "book_info" then
+        self.ui:handleEvent(Event:new("ShowBookInfo"))
     elseif action == "book_status" then
         self.ui:handleEvent(Event:new("ShowBookStatus"))
     elseif action == "page_jmp_fwd_10" then