Fixed heatbed from 90deg to 120deg

Repetier limited Heatbed to 90degC MAX.  #define HEATED_BED_MAX_TEMP 90
Now changed to #define HEATED_BED_MAX_TEMP 120 (though our heatbeds top
out around 110-115degC - perfect for ABS with Hairspray or kapton)
alowing you to set 110 or higher