Move ICS-engine analyze and AnalyzeGame code to shared back-end

Move ICS-engine analyze and AnalyzeGame code to shared back-end

This code was still duplicated between WB and XB in the front-ends.
Because of its incorporation in AnalyzeModeEvent the 'middle-end'
function AnalyzeModeProc could be eliminated. AnalyzeModeEvent was made
to return an int to flag its success, and keep the JAWS code based
on it out of XBoard.
 The AnalyzeGame code  is now incorporated in AnalyzeFileEvent().