Setting scope allows to upload only application from a ZIP that contains
both SD/BL and App. This is useful for Secure DFU when SD/BL update
succeeds but App upload fails. Repeating SD/BL is not possible as the BL
version check fails.
UART now checks the RX characteristic properties and:
1) it will use long write if WRITE REQUEST is set,
2) it will divide the text into up to 20-bytes packets
Also the app background has been fixed.