Improvement and fixes to FTDI touch UI

- Fixed incorrect LCD text string
- Fixed incorrect refresh of filament change screens
- Allow host control via touch UI
- Updates to leveling menu
- Modified ExtUI::isPrinting() to check if the job timer is running
- Added ExtUI method to check whether a host print is paused

Marlin/src/lcd/extui/ui_api.h

@@ -302,6 +302,7 @@ namespace ExtUI {
   bool isPrintingFromMediaPaused();
   bool isPrintingFromMedia();
   bool isPrinting();
+  bool isPrintingPaused();
 
   void printFile(const char *filename);
   void stopPrint();