Split out default CATCH_CONFIG_CONSOLE_WIDTH into its own header

This means that code that uses it no longer has to include all of
catch_config.hpp, which seems to provide significant reduction in
size of unoptimized compilation of the final static library.

src/catch2/catch_config.hpp

@@ -15,10 +15,6 @@
 #include <vector>
 #include <string>
 
-#ifndef CATCH_CONFIG_CONSOLE_WIDTH
-#define CATCH_CONFIG_CONSOLE_WIDTH 80
-#endif
-
 namespace Catch {
 
     struct IStream;