Moving Board.Letters to Vertex.Letters
Catching exception in Vertex.ToString()
Revert "Catching exception in Vertex.ToString()"

This reverts commit 2cb35e6291d958024f58f4e81176073ece33de2d.
Revert "Revert "Catching exception in Vertex.ToString()""

This reverts commit 5e1984cf247f4faa788a00c9f2858d79afcea5ae.