MedieInfo U2.13 FinalSlim

Compile first and compare with U2.12.

Test:
- Media folder modal
- JPG upload/delete
- Slide editing
- MQTT plain payload and JSON fields
- Image, slide and mixed playback
- Language flags
- OTA

Current MQTT commands:
start
stop
next
prev
show N
slide N
folder NAME
slideshow
playlist slides
playlist images
playlist mixed
playlist stop
playlist next
playlist prev
