added a chat window to keep track of multiple conversations

added a chat window to keep track of multiple conversations

The chat-window patch affects:
winboard.c, backend.c, winboard.rc, resource.h, backend.h, and adds
the file winboard/wchat.c, which also affects makefile.gcc and makefile.ms.

In addition I added a new option -keepAlive, which affects
common.h (in addition to winboard.c and backend.c).

As I had to modify backend.h, I also defined the -reset option type there,
which we are going to add later. This required some changes
to suppress warnings in wsettings.c.