Split back-endish part off xoptions.c, and move to dialogs.c

Split back-endish part off xoptions.c, and move to dialogs.c

Some MenuProcs for dialogs were also moved to dialogs.c from menus.c.
MoveTypeInProc which is an event handler for the board widget,
was moved to xboard.c, where it can be static.

Identify dialogs by enum type
 A new header dialogs.h is created, which defines an enum type DialogClass
 that is now used to identify the various dialogs done by GenericPopUp.
 The prototypes for GenericPopUp/PopDown, and other globals shared by the
 dialogs code and other modules can go in here as well.
Remove ClearTextWidget
 This did the same as SetWidgetText with an empty string.
Split X-code from PutText
Split back-end part from MoveTypeInProc
Take set-title out of comment popup
Sort MenuProcs in dialogs.c with their support functions
Declare globals in dialogs.c with functions where they belong
Add prototypes to dialogs.h
Move prototypes and globals from xoptions.c to dialogs.h
Make accessor DialogExists for dialog shells
Add dialogs.c to makefile: compiles and runs!
Combine 3 calls into front-end to InitDrawingParams
Move EditCommentProc and ICSInputBoxProc to dialogs.c
Pass option list as argument to GenericUpdate and GenericReadOut
Shorten argument name from currentOption to opts
 This to prevent confusing it with the global variable of that name.