Modified low friction spool holder for ultimaker 2

Small modifications to the excellent low friction spool holder for ultimaker 2.

I recently used another filament supplier which uses 9cm wide spools which don't fit, I created a longer core2 (which has a length of 70.9 mm) and also created a smaller nut (which consumes less space behind the printer) both are a drop in replacement for the 608 bearing version.

Apparently the colorfabb 2Kg spools are even 10cm wide. So on request I created a 91.9mm extra long version which should be suitable