SDCard Fixes / M39 Command

Trying to catch back up again and figure out where I left off. Little bit of a backlog.

Fixed a few SD menu performance issues and crashes.
Added an M39 command to print Sdcard info (note: Needed a new printNumber for 64bit) works with JSON output specifically like: https://reprap.org/wiki/G-code#M39_Report_SD_card_information
Moved sdcard's class from Repetier.h into its own header file alongside SDCard.cpp

repetier / Repetier-Firmware