SPIFFS and ESP SD card file browser

[probonopd]

SPIFFS and SD card file browser file browser so that we can store and manage more than one GCODE file on the SD card.

• For SD card, we could store all GCODEs ever sent to the printer as long as space permits
• For SPIFFS, we should only store GCODE which was specifically uploaded for this purpose (e.g., some simple calibration GCODE) in order to leave enough space

Priority should be on SD card, SPIFFS is nice to have.

[probonopd]

Possibly this can be de-prioritized if we have #131 working.

[GMagician]

I've tryed some time ago to store a gcode into sd via repetier...unthinkable

[probonopd]

This ticket is about storing on the ESP SD card, not on the printer SD card. #131 is about storing on the printer SD card.

[GMagician]

SPIFF browser is already present (/editor) but not too much flash to store a lot of files

[probonopd]

Yes, we need a way to print from there, and we need this for SD.

[GMagician]

Print from /editor is almost impossible, it's linked in binary form I think and modify it is not as easy as it may seems