fix show hidden flag not persistent between restart

This should fix bug reported in comments of #278.

frontend/apps/filemanager/filemanager.lua

@@ -36,11 +36,14 @@ function FileManager:init()
 		},
 		VerticalSpan:new{ width = Screen:scaleByDPI(10) }
 	}
-
+	
+	local g_show_hidden = G_reader_settings:readSetting("show_hidden")
+	local show_hidden = g_show_hidden == nil and DSHOWHIDDENFILES or g_show_hidden
 	local file_chooser = FileChooser:new{
 		-- remeber to adjust the height when new item is added to the group
 		path = self.root_path,
 		show_parent = self.show_parent,
+		show_hidden = show_hidden,
 		height = Screen:getHeight() - self.banner:getSize().h,
 		is_popout = false,
 		is_borderless = true,
@@ -92,6 +95,7 @@ end
 
 function FileManager:toggleHiddenFiles()
 	self.file_chooser:toggleHiddenFiles()
+	G_reader_settings:saveSetting("show_hidden", self.file_chooser.show_hidden)
 end
 
 function FileManager:onClose()

frontend/ui/widget/filechooser.lua

@@ -9,7 +9,7 @@ local FileChooser = Menu:extend{
 	no_title = true,
 	path = lfs.currentdir(),
 	parent = nil,
-	show_hidden = DSHOWHIDDENFILES,
+	show_hidden = nil,
 	show_filesize = DSHOWFILESIZE,
 	filter = function(filename) return true end,
 }