Add support for "Scandinavian style" crosswords

[heatherleaf]

In Scandinavian style crosswords the clues are written directly in the crossword. To support this we need to:

• be able to have two clues in the same cell (one horizontal and one vertical) (#8)
• automatically(?) decide which cell should contain the clue, e.g.:
  • vertical words: the cell immediately above
  • horizontal words: the cell immediately to the left (unless there is no cell there, in which case the one above)
  • if there is no cell above/to left, we can perhaps use the one to the left/above - but then we might end up in 3-4 clues in the same cell
• if a clue is not in the "normal" place we need arrows from the clue to the word (#7)