disable hinting temporarily in config dialog and flipping mode and cropping dialog

Since hinting is of little use in these situations.

frontend/ui/reader/readerhinting.lua

@@ -0,0 +1,19 @@
+
+ReaderHinting = EventListener:new{
+	hinting_states = {}
+}
+
+function ReaderHinting:onSetHinting(hinting)
+	self.view.hinting = hinting
+end
+
+function ReaderHinting:onDisableHinting()
+	table.insert(self.hinting_states, self.view.hinting)
+	self.view.hinting = false
+	return true
+end
+
+function ReaderHinting:onRestoreHinting()
+	self.view.hinting = table.remove(self.hinting_states)
+	return true
+end