interface: Support localised cell text

This should allow translators to choose whether to display the game
board in their local numerals, or in the default Arabic numerals.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #13
1 job for 13-localised-board in 2 minutes and 23 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #236193
build-and-test

00:02:23