33 add support for more ibis telegrams

[chyzhykio]

Closes #33

New telegrams

• Special char lE / qE — a route with "sc": 0–99 in routes.ndjson sends a special character (logo, unsupported
  route number) in place of the line number.
• DS021, DS021neu, DS021T — one telegram per display, set up in a new optional displays block in
  config.json. addr, display_type (external / internal), enabled, a per-display
  show_start_and_end_stops, plus mode/width (DS021), font (DS021neu) and cycle* (DS021T).
  *DS021T sends a single page for now.
• DS009 — stop_board_telegram alternative to DS003c for the internal display.

Changes in behaviour

• "nlt": true now clears the line display instead of sending nothing, which left the previous route number
  on it. It sends nlt_data from config.json, or zeros (l000 / q0000) when that is not set.
• Telegrams go out as soon as the driver changes the route or direction, not at the next 10 s tick.
• A direction with "f": [] raises error 308 instead of crashing the main loop with E700.

Config check

• The structure checker now accepts nested arrays and objects, and repeated keys are caught inside every object,
  not only at the top level.
• 5 new messages in lib/lang.py