ENH: Separate VS flag table type

Move the cmVS7FlagTable type out of the VS generators and rename it to
cmIDEFlagTable.  It will be useful for other generators.

Source/cmLocalVisualStudio7Generator.h

@@ -18,7 +18,7 @@
 #define cmLocalVisualStudio7Generator_h
 
 #include "cmLocalVisualStudioGenerator.h"
-#include "cmVisualStudioGeneratorOptions.h" // to get cmVS7FlagTable
+#include "cmVisualStudioGeneratorOptions.h"
 
 class cmTarget;
 class cmSourceFile;