Modified Turn Response Protocol, added handling for SIGPIPE, changed placeholder images

The "outcome" of a move is now listed as:

TYPE [ATTACKER_RANK] [DEFENDER_RANK]

Where ATTACKER_RANK and DEFENDER_RANK will be present if TYPE is one of: KILLS, DIES, BOTHDIE, and indicate the ranks of the pieces involved.
This involved adding a class MovementResult, which stores the ranks of pieces in addition to an enum, replacing the enum Board::MovementResult

The sample agent "forfax" was causing broken pipes, which caused the manager program to exit.
I added a handler for SIGPIPE in manager/main.cpp to ensure that the manager program reports a DEFAULT victory to the other AI, and exits gracefully.
However, I still don't know WHY forfax causes broken pipes, but hopefully its a problem with forfax and not with the manager program.

I edited the images used by the graphical display to show the ordered ranks of the pieces, rather than some obscure characters.
Unfortunately I have just realised that the enum used for Piece::Type stores ranks in the wrong order.
In the actual game, LOWER numbers are better, in my enum, HIGHER numbers are better.
To make things more confusing, I made the printed ATTACKER_RANK and DEFENDER_RANK correspond to the traditional numbering, not the enum numbering...