ui: stop showing the all-FF record marker as a field; label it in the diff (v3.1.4)

A profile check comparing an empty PNN record against a populated one
showed a cryptic 'Empty: yes' row: the decoders return {empty: true} for
an all-FF record and efFlatten() rendered that marker as a pseudo-field
('empty' prettified to 'Empty', the boolean as 'yes').

- efFlatten() skips the marker (the decoded views already show their own
  translated 'empty' note next to the record).
- efDiffData() fills the cells of a side that decodes to an all-FF record
  with 'Empty (all FF)' (RU: 'Пусто (только FF)') instead of leaving them
  blank; a field merely missing from a non-empty record stays blank.
- tests: efFlatten marker, one-sided and both-sided empty diffs, and the
  PNN case from the report; help EN/RU note the new text.
- sw.js simple-v239.

pysim_simple_server/server.py

@@ -28,7 +28,7 @@ from osmocom.tlv import BER_TLV_IE
 from osmocom.utils import rpad
 
 
-VERSION = '3.1.3'
+VERSION = '3.1.4'
 
 MAX_ENVELOPE_SEGMENTS = 5  # max SMS segments for outgoing C-APDU in ENVELOPE